MANUAL  OF 

MEDICAL  RESEARCH 

LABORATORY 


WAR  DEPARTMENT    :     :    AIR  SERVICE 

DIVISION  OF  MILITARY  AERONAUTICS 

WASHINGTON,  D.  C. 


WASHINGTON 

GOVERNMENT  PRINTING  OFF1CK 
1918 


MEDICAL  RESEARCH  LABORATORY. 


W.  H.  WILMEB,  Colonel,  M.  C.,  N.  A. 
HEADS    OF  MEDICAL   RESEARCH    LABORATORY    DEPARTMENTS. 

Car  dio- vascular : 

JAMES  L.  WHITNEY,  Major,  M.  R.  C. 

Neurology  and  psychiatry: 

STEWART  PATON,  Major,  M.  R.  C. 

Ophthalmology: 

CONRAD  BERENS,  Jr.,  Captain,  M.  R.  C. 

Otology : 

EUGENE  R.  LEWIS,  Lieutenant  Colonel,  M.  C.,  N,  A. 
Physiology: 

EDWARD  C.  SCHNEIDER,  Major,  Sanitary  Corps,  N.  A.  • 

Psychology : 

KNIGHT  DUNLAP,  Major,  Sanitary  Corps,  N.  A. 
2 


CONTENTS. 

Page. 
ALTITUDE  PHYSIOLOGY 7 

Altitude  sickness.  Oxygen  want,  the  cause.  Adaptations  to  high  alti- 
tudes'. Blood  changes.  Circulation  reactions,  pulse  rate,  arterial  pres- 
sure, venous  pressure,  capillary  pressure,  and  blood  flow.  Respiration. 
Arterial  blood  oxygen  pressure.  Value  of  the  factors  of  acclimatization. 
Physical  fitness  and  ability  to  withstand  high  altitudes.  Staleness. 

PHYSIOLOGY  OF  REBREATHING  AND  AVIATION 38 

Respiration.  Circulation.  Hemoglobin.  Value  of  the  several  compen- 
satory factors. 

TABLE:   RELATION  OF  ALTITUDE,  PRESSURE  AND  OXYGEN 70 

THE  EFFECTS  OF  Low  ATMOSPHERIC  PRESSURE  ON  THE  CIRCULATORY  SYSTEM.  75 
The  physiology  of  circulation.  Relation  of  vasomotor  control  to  the  heart. 
Failure  to  compensate.  Insufficient  compensation.  Collapse.  Heart 
strain.  Temporary  indisposition.  Physiology  of  exercise  compared 
with  aviation.  Fainting.  Arteriosclerosis.  Arrythmia.  Valvular  dis- 
ease. Athletic  hearts. 

OTOLOGY 97 

OPHTHALMOLOGY 133 

Selection  of  the  aviator.  Ophthalmological  examination  of  applicants  for 
detail  in  the  Department  of  Military  Aeronautics.  Value  of  the  eye  in 
aviation.  The  case  of  the  flier  and  th'e  effect  of  altitude  and  the  strain 
of  flying  on  the  eye.  Goggles.  Ophthalmological  examination  of  the 
flier  during  low  oxygen  tension.  Preliminary  experiments. 

PSYCHOLOGY 163 

The  relation  of  psychology  to  the  aviator.  Psychological  examination 
during  rebreathing.  The  psychological  effects  of  oxygen  deficiency. 
Practice.  The  limitations  imposed  by  the  practical  requirements  of 
rating.  Apparatus  for  the  Standard  Test.  Instructions.  Motor  tenden- 
cies, symbols,  and  their  significance.  Rating.  The  psychological  quali- 
fications of  the  flier. 

NEUROLOGY  AND  PSYCHIATRY *  200 

THE  REBREATHING  MACHINE 212 

THE  LOW-PRESSURE  CHAMBER 213 

THE  CLASSIFICATION  EXAMINATION 215 

DIRECTIONS  FOR  THE  CLASSIFICATION  EXAMINATION 220 

Routine  for  examination  and  record  keeping.  Directions  to  clinician. 
The  diagnosis  of  valvular  heart  disease.  Eye  examination.  Instruc- 
tions to  the  psychologist.  Instructions  to  the  physiologist.  Prepara- 
tion and  care  of  the  rebreathing  machine  and  recording  apparatus.  The 
Henderson-Orsat  Gas  Analyzer. 

3 


PREFACE. 


Though  the  principles  of  aeronautics  were  clearly  enunciated  by 
Samuel  Johnson  159  years  ago  in  his  Rasselas,  Prince  of  Abysinia,  it 
was  not  until  within  the  last  decade  that  air  flights  began  to  be  practi- 
cal. During  these  years  infinite  time  and  thought  have  been  spent  upon 
the  machine.  The  pitch  of  the  screw,  the  angle  of  attack,  the  stream 
line,  the  admixture  of  gasoline  and  air,  etc.,  have  all  been  studied  with 
mathematical  accuracy. 

But  the  value  of  the  human  machine  is  just  beginning  to  be  properly 

recognized.    A  slack  control  wire  is  not  more  dangerous  than  a  weak 

eye  muscle,  a  poor  mixture  of  gas  and  air  is  not  more  serious  than  a 

4  flier  with  po9r  adaptive  respiration.    And  a  poor  compression  in  the 

cylinder  is  not  of  such  vital  consequence  as  a  weak  heart  muscle. 

The  Laboratory,  which  is  the  workshop  of  the  Medical  Research 
Board  of  the  Air  Service,  investigates  "  all  conditions  which  affect 
the  efficiency  of  pilots";  classifies  fliers  not  only  according  to  their 
efficiency,  but  also  according  to  their  ability  to  stand  diminished  oxy- 
gen; and  instructs  Flight  Surgeons  and  Physical  Directors  in  the 
reactions  of  the  human  system  to  oxygen  want. 

This  manual  is  the  result  of  the  work  done  in  the  Laboratory  and  it 
is  intended  for  the  information  and  instruction  of  those  who  are 
interested  in  the  medical  problems  of  aviation.  In  these  brief  pages 
it  has  been  impossible  to  go  fully  into  a  subject  so  new  and  so  large, 
but  it  is  the  earnest  hope  that  the  faithful  painstaking  work  of  the  de- 
partment heads  and  their  assistants  may  be  of  service  in  stimulating 
the  study  of  conditions  that  are  of  such  vital  economic,  military,  and 
human  value. 

WILLIAM  H.  WILMER,  M.  C.,  N.  A., 

Officer  in  Charge. 

MEDICAL  RESEARCH  LABORATORY, 

Mineola,  L.  /.,  July  6, 1918. 

5 


ORGANIZATION    OF    MEDICAL    RESEARCH    LABORATORY. 

In  accordance  with  paragraph  113,  S.  O.  243,  A.  G.  O.,  October  18, 
1917,  the  following  officers  were  directed  to  report  to  the  Chief  Sur- 
geon, Aviation  Section,  Signal  Corps,  for  assignment  to  duty  as 
members  of  a  medical  research  board:  Maj.  John  B.  Watson,  S.  O. 
R.  C. ;  Maj.  Eugene  R.  Lewis,  M.  R.  C. ;  Maj.  William  H.  Wilmer,  M. 
R,  C.;  Maj.  Edward  G.  Seibert,  M.  R.  C. 

Dr.  Yandell  Henderson  was  added  to  this  board  in  civilian  capacity 
nnd  was  constituted  chairman  of  the  board. 

The  powers  delegated  to  the  board  were  as  follows : 

This  board  shall  have  discretionary  powers : 

(1)  To  investigate  all  conditions  which  affect  the  efficiency  of  pilots. 

(2)  To  institute  and  carry  out,  at  flying  schools  or  elsewhere,  such  experi- 
ments and  tests  as  will  determine  the  ability  of  pilots  to  fly  in  high  altitudes. 

(3)  To  carry  out  experiments  and  tests,  at  flying  schools  or  elsewhere,  to 
provide  suitable  apparatus  for  the  supply  of  oxygen  to  pilots  in  high  altitudes. 

(4)  To  act  as  a  standing  medical  board  for  the  considei'ation  of  all  matters 
relating  to  the  physical  fitness  of  pilots. 

In  accordance  with  this  authority,  the  board  instituted  the  fol- 
lowing departments: 

Otology — Lieut.  Col.  E.  R.  Lewis. 

Cardio-vascular Maj.  James  L.  Whitney. 

Physiology : Maj.  Edward  C.  Schneider. 

Psychology Maj.  Knight  Dunlap. 

Psychiatry  and  neurology Maj.  Stewart  Paton. 

Ophthalmology Capt.  Conrad  Berens,  Jr. 

The  immediate  military  problem  of  classification  of  aviators  was 
preceded  by  certain  necessary  research  sufficient  to  establish  basis  of 
such  classification. 

The  present  organization  comprises  the  main  laboratory  at  Hazel  - 
hurst  Field,  with  20  branch  laboratories  at  flying  schools  and  ground 
schools,  8  of  which  are  now  in  active  operation. 

Officers  are  now  under  instruction  at  the  main  laboratory  for  the 
remaining  stations. 

E.  G.  SEIBERT, 
Lieut.  Col.  M.  67.,  N.  A. 

Secretary  Medical  Research  Board. 
6 


MEDICAL  ASPECTS  OF  AVIATION. 
I.— ALTITUDE  PHYSIOLOGY. 

In  recent  years  our  knowledge  of  the  conditions  pertaining  to  life 
at  high  altitudes  has  been  enriched  by  careful  scientific  investiga- 
tions. The  majority  of  these  have  been  carried  out  on  Monte  Rosa 
in  Europe  and  on  Pike's  Peak  in  the  United  States.  Further  con- 
tributions come  from  studies  made  in  pneumatic  cabinets  in  which 
the  atmospheric  pressure  can  be  reduced  to  any  degree  correspond- 
ing to  known  heights. 

The  physiologic  effects  of  altitude  on  man  and  other  animals  have 
a  threefold  interest.  The  purely  scientific  aspects  of  the  life  under 
conditions  of  low  barometric  pressure  are  themselves  deserving  of 
careful  investigation.  The  fact  that  altitude  plays  a  part  in  thera- 
peutics and  forms  a  feature  of  climatology,  as  applied  by  medicine, 
furnishes  another  reason  why  the  subject  should  be  placed  on  a  ra- 
tional basis.  While  the  coming  into  prominence  of  aviation  which 
requires  a  man  to  ascend  into  the  air  as  the  bird,  frequently  to  mod- 
erate and  sometimes  to  great  altitudes,  furnishes  a  third  reason  why 
we  should  know  what  constitutes  fitness  for  life  in  rarefied  air.  As 
soon  as  an  attempt  is  made  to  interpret  the  physiologic  phenomena 
of  altitude  in  terms  of  their  causes  difficulties  arise.  The  reason  for 
contradictory  theories  is  to  be  found  in  the  complexity  of  the  factors 
which  enter  into  the  environment  at  high  altitudes.  Among  the  cli- 
matic variables  are  the  low  atmospheric  pressure  with  its  low  partial 
pressure  of  oxygen,  the  peculiarities  of  the  sunshine,  low  temperature 
and  humidity,  the  high  wind,  the  electric  conditions  of  the  atmo- 
sphere, and  ionization.  It  has  been  found  difficult  to  study  these  fac- 
tors one  at  a  time,  but  with  the  use  of  the  pneumatic  cabinet  it  is 
possible  to  eliminate  all  factors  except  lowered  barometric  pressure 
and  also  to  study  the  added  influence  of  other  altitude  factors.  The 
consensus  of  opinion  held  is  that  the  physiologic  effects  noted  at  high 
altitudes  are  due  to  the  lack  of  oxygen  resulting  from  the  lowered 
partial  pressure  of  oxygen. 

It  is  elearty  established  to-day  that  high  altitudes  or  low  baro- 
metric pressure  when  first  encountered  may  interfere  with  the  normal 
workings  of  the  human  machine.  A  sudden  disturbance  of  any  sort 
of  the  bodilj-  functions  is  usually  manifest  by  symptons  of  illne&s. 


8  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

Those  disturbances  brought  on  by  change  of  altitude  cause  the  so- 
called  mountain  sickness,  or,  better,  altitude  sickness,  the  symptoms 
of  which  are  generally  so  mild  that  they  may  be  entirely  overlooked 
by  the  unobservant.  Mankind  differs  greatly  in  the  power  of  ad- 
justment to  changes  of  environment.  Hence,  it  is  found  that  moun- 
tain sickness  befalls  some  individuals  at  a  lower,  others  at  a  higher 
altitude,  but  it  is  also  certain  that  no  one  who  proceeds  beyond  a 
certain  elevation — the  critical  line  for  him — escapes  the  malady.  An 
elevation  of  10.000  feet  or  even  less  might  provoke  it  in  some,  others 
may  escape  the  symptoms  up  to  14,000  feet,  while  only  a  very  few, 
possessed  of  unusual  resisting  power,  can  without  much  distress 
venture  upward  to  19,000  feet.  The  symptoms  of  mountain  sickness 
depend  not  only  on  the  nature  of  the  individual  and  his  physical 
condition,  but  also  on  various  intricate  contingencies,  especially  on 
the  amount  of  physical  exertion  made  in  ascending;  that  is,  on 
whether  the  ascent  is  performed  by  climbing  or  by  passive  carriage 
on  horse,  on  railway  train,  or  in  an  aeroplane. 

There  are  two  forms  of  mountain  sickness ;  the  acute  and  the  slow. 
The  acute,  due  to  going  too  far  beyond  the  individual  critical  line, 
breaks  out  suddenly  on  entrance  into  the  rarefied  air ;  the  slow  mani- 
fests itself  later  and  other  debilitating  causes  besides  the  barometric 
depression  often  contribute  to  produce  it. 

The  acute  form  is  characterized  by  a  rapid  pulse,  nausea,  vomiting, 
physical  prostration  which  may  even  incapacitate  one  for  movement, 
livid  color  of  the  skin,  buzzing  in  the  ears,  dimmed  sight,  and  faint- 
ing fits. 

In  the  slow  form  of  mountain  sickness,  which  may  be  called  the 
normal  type,  the  newcomer  at  first  complains  of  no  symptoms.  -In 
fact,  when  questioned  he  says  he  feels  fine.  Occasionally  he  may 
report  that  on  stooping  over  and  raising  himself  up  again,  he  feels 
dizzy  and  has  a  visual  sensation  of  blackness.  Even  at  this  time  on  ex- 
amination there  is  found  blueness  of  the  lips,  edges  of  the  eyelids, 
gums,  and  under  the  finger  nails.  Some  hours  later  he  begins  to 
feel  "  good  for  nothing  "  and  disinclined  for  exertion ;  to  express  it 
differently,  he  finds  that  he  feels  somewhat  weak  and  exhausted. 
He  goes  to  bed  and  has  a  restless  and  troubled  night  and  wakes  up 
next  morning  with  a  severe  frontal  headache.  Many  find  that  the 
headache  begins  to  develop  toward  evening  or  during  the  night  of 
the  first  day.  Following  it  there  may  be  vomiting  and  frequently  a 
sense  of  depression  in  the  chest.  The  patient  may  feel  slightly  giddy 
on  arising  from  bed  and  any  attempt  at  exertion  increases  the  head- 
ache which  is  nearly  always  confined  to  the  frontal  region.  On 
examination  the  face  may  be  slightly  cyanosed,  the  eyes  look  dull 
and  heavy  and  there  may  be  a  tendency  for  them  to  water.  The 
tongue  is  furred,  the  pulse  is  nearly  always  high,  being  generally  in 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  9 

the  neighborhood  of  100  or  over.  The  temperature  is  normal  or 
slightly  under.  The  patient  often  feels  cold  and  shivery.-  All  ap- 
petite is  lost,  some  have  diarrhoea  and  abdominal  pain.  A  tendency 
to  periodic  breathing  is  observed  in  many  and  physical  exertion  is 
accompanied  by  great  hyperpnoea. 

There  are  wide  divergencies  from  this  slow  or  normal  type  of 
mountain  sickness.  Dr.  Ravenhill  has  grouped  these  into  two  classes, 
(1)  those  in  which  cardiac  symptoms,  and  (2)  those  in  which  nerv- 
ous symptoms  predominate.  Neither  is  common.  The  cardiac  type 
is  well  illustrated  by  one  of  Dr.  Ravenhill's  cases.  An  English 
gentleman  in  the  Andes  Mountains  ascended  from  sea  level  to  15,400 
feet  in  42  hours.  Three  years  before  he  had  lived  at  the  same  alti- 
tude for  a  period  of  three  months  and  had  been  in  good  health  the 
whole  time.  He  seemed  in  good  health  upon  arrival ;  he  kept  quiet, 
ate  sparingly,  and  went  to  bed  early,  but  awoke  the  next  morning 
feeling  ill  with  symptoms  of  the  normal  type.  Later  in  the  day  he 
began  to  feel  very  ill.  In  the  afternoon  his  pulse  rate  was  144, 
respirations  40.  Later  in  the  evening  he  became  very  cyanosed,  had 
acute  dyspnoea  and  evident  air  hunger,  all  the  extraordinary  mus- 
cles of  respiration  being  called  into  play.  His  heart  sounds  were 
very  faint;  the  pulse  irregular  and  of  small  tension,  thus  presenting 
a  typical  picture  of  a  failing  heart.  The  condition  persisted  during 
the  night;  he  coughed  up  with  difficulty  and  vomited  at  intervals. 
He  was  sent  down  on  an  early  train  the  next  morning.  At  12,000 
feet  he  was  considerably  better  and  at  7,000  feet  he  was  nearly  well. 
Dr.  Ravenhill  thought  that  he  would  have  died  had  he  remained 
another  day. 

The  nervous  type  of  mountain  sickness  in  its  simplest  form  con- 
sists of  the  feeling  of  a  nervous  excitation  and  buoyancy.  Some 
feel  as  though  they  are  being  lifted  into  the  air  as  by  a  balloon^ 
There  may  be  a  tendency  to  twitching  of  the  lips  and  trembling  of 
the  limbs.  In  severe  cases  these  may  lead  on  to  violent  spasmodic 
movements  of  the  limbs  and  even  convulsions.  Vertigo  may  be-  a 
prominent  symptom,  though  it  is  very  rarely  pronounced. 

The  symptoms  of  mountain  sickness  persist  for  one,  two,  and  three 
days  and  then  gradually  disappear  as  the  adaptive  reactions  to  high 
altitude  occur.  The  action  of  gradually  developing  want  of  oxygen 
at  very  high  altitudes  is  very  insidious  as  dangerous  effects  may 
develop  with  a  dramatic  suddenness.  Two  now  historic  experiences 
illustrate  this.  In  1862  the  well  known  meteorologist,  Glaisher,  and 
his  assistant,  Coxwell,  ascended  in  a  balloon.  Glaisher  first  noticed 
at  an  altitude  of  about  26,000  feet  that  he  could  not  read  his  instru- 
ment properly.  Shortly  after  this  his  legs  were  paralyzed  and  then 
his  arms,  though  he  could  still  move  his  head.  Then  his  sight  failed 
entirely  and  afterwards  his  hearing  and  he  became  unconscious.  His 


10  MANUAL  OF  MEDICAL  EESEAECH   LABOBATORY. 

companion  meanwhile  found  that  his  arms  were  paralyzed,  but  that 
he  was  still  able  to  seize  and  pull  the  rope  of  a  valve  with  his  teeth — 
this  permitted  gas  to  escape — so  that  the  balloon  descended.  As 
Glaisher  recovered  consciousness,  he  first  heard  his  companion's  voice 
and  then  was  able  to  see  him,  after  which  he  quickly  recovered.  The 
balloon,  during  the  ascent,  reached  an  altitude  of  about  30,000  feet. 
The  second  of  these  historic  experiences  is  found  in  a  graphic  account 
given  by  Tissandier,  the  sole  survivor  of  a  party  of  three  in  a  fatal 
balloon  ascent  in  1875. 

"  I  now  come  to  the  fateful  moments  when  we  were  overcome  by  the  terrible 
action  of  reduced  pressure.  At  22,900  feet  (320  mm.)  we  were  all  below  in 
the  car — torpor  had  seized  me.  My  hands  were  cold  and  I  wished  to  put  on 
my  fur  gloves;  but,  without  my  being  aware  of  it,  the  action  of  taking  them 
from  my  pocket  required  an  effort  which  I  was  unable  to  make.  At  this  height 
I  wrote,  nevertheless,  in  my  notebook  almost  mechanically  and  reproduce  liter- 
ally the  following  words  though  I  have  no  very  clear  recollection  of  writing 
them.  They  are  written  very  illegibly  by  a  hand  rendered  very  shaky  by  the 
cold:  "My  hands  are  frozen.  I  am  well.  We  are  well.  Haze  on  the  horizon, 
with  small  round  cirrus.  We  are  rising.  Croc6  is  panting.  We  breathe 
oxygen.  Sivel  shuts  his  eyes.  Croc6  also  shuts  his  eyes.  I  empty  aspirator, 
1.20  p.  m.,  — 7  to  — 11  degrees,  barometer  320.  Sivel  is  dozing,  1.25,  — 11 
degrees,  barometer  300.  Sivel  throws  ballast  (last  word  scarcely  legible)." 
I  had  taken  care  to  keep  absolutely  still  without  suspecting  that  I  had  already 
perhaps  lost  the  use  of  my  limbs.  At  24,600  feet  the  condition  of  torpor  which 
overcomes  one  is  extraordinary.  Body  and  mind  become  feebler  little  by 
little,  gradually  and  insensibly.  There  is  no  suffering.  On  the  contrary  one 
feels  an  inward  joy.  There  is  no  thought  of  the  dangerous  position ;  one  rises 
and  is  glad  to  be  rising.  The  vertigo  of  high  altitude  is  not  an. empty  word; 
but  so  far  as  I  can  judge  from  my  own  impressions  this  vertigo  appears  at  the 
last  moment,  and  immediately  precedes  extinction,  sudden,  unexpected,  and 
irresistible.  I  soon  felt  myself  so  weak  that  I  could  not  even  turn  my  head  to 
look  at  my  companions.  I  wished  to  take  hold  of  the  oxygen  tube  but  found 
that  I  could  not  move  my  arms.  My  mind  was  still  clear,  however,  and  I 
watched  my  aneroid  with  my  eyes  fixed  on  the  needles  which  soon  pointed  to 
290  mm.  and  then  to  280.  I  wished  to  call  that  we  are  now  at  26,000  feet, 
but  my  tongue  was  paralyzed.  All  at  once  I  shut  my  eyes  and  fell  down  power- 
less and  lost  all  further  memory.  It  was  about  1.30." 

The  balloon  ascended  28,820  feet  and  then  descended.  Tissandier. 
recovered  but  his  companions  lost  their  lives  in  the  ascent.  These 
extreme  cases  are  cited  here  in  order  to  bring  to  the  attention  of 
aviators  the  risk  in  going  to  extremely  high  altitudes  without  oxygen. 


The  essential  cause  of  altitude  sickness  is  lack  of  oxygen.  The 
probability  of  this  explanation  was  first  clearly  pointed  out  by 
Jourdanet,  but  it  was  Paul  Bert,  in  1878,  who  first  furnished  clear 
experimental  proof  that  the  abnormal  symptoms  and  dangers  depend 
on  the  imperfect  aeration  of  the  arterial  blood  with  oxygen.  He 


MANUAL   OF   MEDICAL  RESEARCH    LABORATORY.  11 

concluded  that  all  the  symptoms  are  simply  those  of  want  of  oxygen. 
Later  observers,  however,  questioned  this  conclusion  and  attributed 
the  symptoms  in  whole  or  in  part  to  other  causes.  Mosso  attributed 
many  of  the  symptoms  to  the  lack  of  carbon  dioxide,  while  Kronecker 
has  invoked  mechanical  factors  as  a  cause.  The  evidence  accumu- 
lated by  more  recent  workers,  botli  on  mountains  and  in  pneumatic 
chambers,  have  definitely  confirmed  Paul  Bert's  conclusion. 

The  call  for  oxygen  in  the  body  comes  from  the  active  cells  of  the 
tissues.  It  has  been  evident  for  sometime  that  the  place  of  oxida- 
tion is  in  the  cells  and  not  in  the  blood  as  was  formerly  maintained. 
Complete  deprivation  of  oxygen  results  in  asphyxiation  and  death. 
The  question  that  naturally  arises  is ;  Is  the  quantity  of  oxygen  taken 
up  by  the  cell,  conditioned  primarily  by  the  needs  of  the  cell  or  by 
the  supply  of  oxygen  '*.  This  has  been  answered  clearly ;  the  cell  takes 
what  it  needs  and  leaves  the  rest.  Therefore,  it  is  important  that 
sufficient  oxygen  be  available  in  the  blood  when  the  demand  is  made 
by  the  tissues.  The  rate  of  flow  and  the  amount  of  oxygen  passing 
from  the  blood  to  the  tissues  depends  on  the  difference  between  the 
pressure  of  oxygen  in  the  blood  and  in  the  tissue.  The  higher  the 
oxygen  pressure  in  the  blood  the  greater  will  be  the  amount  of 
oxygen  passing  from  the  blood  of  the  capillaries  into  the  tissues  in  a 
given  unit  of  time.  Oxygen  diffuses  from  the  place  of  higher  pres- 
sure to  the  place  of  no  pressure  or  low  pressure.  In  the  active  tis- 
sues the  oxygen  tension  is  always  low  and  it  is  usually  supposed 
there  is  then  no  oxygen  pressure  at  all  inside  the  cells.  The  dissocia- 
tion of  oxygen  from  the  hemoglobin  of  the  blood  occurs  with  great 
rapidity,  but  it  is  greatest  where  the  differences  in  pressure  are 
greatest.  It  follows,  therefore,  that  the  oxygen  pressure  in  the  blood 
must  be  sufficiently  high  to  supply  the  needs  of  the  cell  in  the  brief 
interval  of  time  that  the  blood  is  passing  through  the  capillaries. 

There  are  many  ways  in  which  the  oxygen  supply  of  the  body  may 
be  reduced.  Whatever  the  method  used  there  will  occur  compensa- 
tory adaptive  reactions  in  the  blood,  the  breathing,  and  the  circula- 
tion for  the  purpose  of  furnishing  the  oxygen  needed  by  the  cell. 
Reduction  of  oxygen  available  to  the  tissues  might  be  brought  about 
by  blood  letting  and  anemia ;  by  the  administration  of  carbon  monox- 
ide or  sodium  cyanide ;  by  life  on  high  mountains,  in  a  balloon,  in  an 
aeroplane  at  high  altitudes,  or  in  pneumatic  cabinets  at  reduced 
pressure ;  by  the  artificial  restriction  of  the  free  influx  of  atmospheric 
air  into  the  lungs;  and  by  artificial  pneumothorax.  Any  of  these 
methods,  if  carried  beyond  a  certain  point,  is  known  to  produce 
death.  If,  on  the  other  hand,  they  are  only  carried  far  enough  to 
give  a  mild  oxygen  hunger,  the  body  will,  as  a  rule,  react  so  as  to 
compensate  for  the  reduction  in  the  oxygen  supply. 


12  MANUAL  OP  MEDICAL  RESEABCH   LABORATORY. 

In  blood  letting,  which  produces  an  artificial  anemia,  the  percent- 
age of  oxygen  in  the  venous  blood  may  be  reduced  from  the  normal 
12  volumes  per  cent  to  4  or  even  3  per  cent.  In  animals  thus  treated 
both  the  circulation  and  the  breathing  will  show  compensatory  activ- 
ity. In  cases  of  anemia  with  a  20  per  cent  reduction  in  hemoglobin 
an  increased  pulse  rate  and  an  increased  respiration  will  be  observed. 
In  cases  of  poisoning  with  carbon  monoxide  and  sodium  cyanide 
there  will  likewise  be  modifications  in  the  blood  flow  and  respiration. 
Kholer  compressed  the  trachea  of  rabbits  by  tying  a  lead  wire 
around  it.  The  animals  recovered  from  the  operation  and  lived  four 
weeks.  Apparently,  to  compensate  for  the  interference  in  breathing, 
there  was  an  increased  rate  of  respiration  and  heart  activity  which 
made  good  the  oxygen  needs  of  the  organism.  In  case  of  artificial 
pneumothorax  the  hemoglobin  of  the  blood  has  been  shown  to  in- 
crease, the  pulse  rate  to  accelerate,  and  the  respiration  to  deepen. 
We  shall  discuss  later  the  adaptive  changes  which  fit  the  human 
mechanism  for  high  altitudes.  These  adaptive  reactions  are  also 
seen  in  the  blood,  in  the  breathing,  and  in  the  circulation. 

While  all  of  the  tissues  of  the  body  are  sensitive,  the  nervous  tis- 
sues are  the  most  sensitive  to  oxygen  want.  The  adaptive  responses 
to  a  lack  of  oxygen  are  undoubtedly  initiated  in  the  central  nervous 
system.  Gaser  and  Loevenhart  find  that  all  of  the  medullary  cen- 
ters in  the  brain  respond  in  the  same  way ;  first,  by  stimulation,  and 
then  by  depression. 

The  mo"re~~cle'mYite  adaptive  altitude  changes  disclosed  by  experi- 
ments are:  (1)  An  increase  in  the  percentage  and  the  total  amount  of 
hemoglobin  in  the  blood  of  the  body  and  also  associated  with  this  a 
redistribution  of  the  red  corpuscles  whereby  a  reserve  supply  is 
thrown  into  the  general  circulation;  (2)  a  fall  in  the  lung  alveolar 
carbon  dioxide  pressure  and  a  rise  in  the  alveolar  oxygen  pressure, 
the  result  of  increased  ventilation  of  the  lungs  due  to  deeper  breath- 
ing; (3)  a  rise  in  the  arterial  blood  oxygen  pressure  which  provides 
a  partial  pressure  of  oxygen  in  the  blood  much  above  the  alveolar 
oxygen  pressure  in  the  lungs;  (4)  an  increase  in  the  rate  of  blood 
flow.  Each  of  these  adaptive  changes  clearly  assures  a  more  adequate 
supply  of  oxygen  for  the  tissues.  The  blood  changes  provide  for 
more  oxygen  in  a  given  unit  volume  of  blood.  The  greater  ventila- 
tion of  the  lungs  permits  a  more  thorough  saturation  of  the  hemo- 
globin with  oxygen  than  would  be  possible  if  the  oxygen  pressure  in 
the  lungs  decreased  proportionately  with  the  fall  in  barometric  pres- 
sure. The  rise  in  arterial  blood  oxygen  pressure  also  means  a  greater 
saturation  of  the  hemoglobin.  The  more  rapid  rate  of  blood  flow 
raises  to  a  limited  extent  the  oxygen  pressure  in  the  blood  passing 
through  the  tissues.  A  discussion  of  these  adaptive  changes  follows : 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  13 

THE   CHANGES   IN  THE  BLOOD  OF   MAN   AT  HIGH  ALTITUDE. 

It  has  long  been  known  that  the  effect  of  life  at  high  altitudes  is 
to  cause  an  increase  in  the  number  of  red  corpuscles  per  cubic  milli- 
meter of  blood  and  an  increase  in  the  hemoglobin  percentage  of  the 
blood.  In  1878  Paul  Bert  predicted  that  the  blood  of  man  and  ani- 
mals living  at  high  altitudes  would  be  found  to  have  a  greater 
oxygen  capacity  than  that  of  corresponding  individuals  living  at 
lower  levels.  He  surmised  that  the  cause  of  this  increase  in  the 
oxygen  carrying  power  of  the  blood  would  be  found  to  be  the  de- 
crease in  the  partial  pressure  of  the  oxygen  in  the  atmosphere  re- 
spired. In  1882  he  gave  an  account  of  some  experiments  in  which 
the  blood  obtained  from  animals  living  at  a  high  altitude  in  Bolivia 
was  found  to  contain  a  larger  percentage  of  oxygen  than  did  blood 
taken  from  animals  at  sea  level.  A  little  later,  in  1890,  Viault  ob- 
served the  increase  in  the  number  of  red  corpuscles  per  cubic  milli- 
meter of  blood  in  himself  and  his  companions  during  a  three  weeks' 
visit  in  Peru  at  an  altitude  of  14,400  feet.  Numerous  subsequent 
observations  which  have  dealt  with  these  phenomena  have  con- 
firmed beyond  question  the  earlier  data.  The  following  figures 
illustrate  the  differences  observed  in  mankind  living  at  different 
altitudes : 

(1)  The  red  corpuscles  vary  at  sea  level  between  4.5  and  5.4 
millions  per  cubic  millimeter;  at  Colorado  Springs,  altitude  6,000 
feet,  between  5.5  and  6.3  millions;   and  on  Pike's  Peak,  altitude 
14,110  feet,  between  6  and  8.2  millions. 

(2)  The  percentage  of  hemoglobin  at  sea  level  varies  between  94 
and  106.  average  100;  in  Colorado  Springs,  105  to  118,  average  110; 
and  on  Pike's  Peak,  120  to  154,  average  144. 

(3)  The  percentage  of  oxygen  capacity  in  the  blood  at  sea  level 
varies  between  17  and  18.7;  in  Colorado  Springs,  20  and  21.7;  and 
on  Pike's  Peak,  approximately  27.4. 

Miss  Fitzgerald  has  found  that  for  every  100  mm.  fall  in  atmos- 
pheric pressure  there  is  an  average  rise  of  about  10  per  cent  in 
hemoglobin  and  that  this  rise  is  approximately  the  same  for 
women  and  men.  There  are  greater  individual  variations  in  the 
total  increase.  It  is  possible  that  under  a  pressure  greater  than 
atmospheric  the  hemoglobin  would  fall  below  100  per  cent.  The 
observations  of  Madame  Bornstein  on  animals  have  apparently  shown 
a  decrease  in  the  percentage  of  hemoglobin  when  they  were  exposed 
to  a  pressure  greater  than  atmospheric. 

Incidentally  it  is  interesting  to  note  that  the  blood  of  the  people 
living  at  high  altitudes  fails  to  show  an  increase  in  leucocytesjbut 
does  show  an  increase  in  the  lymphocyte  index.  Thus  at  sea  level 
this  index  averages  37;  at  Colorado  Springs  (6,000  feet)  42.5;  and 


14 


MANUAL   OF   MEDICAL   RESEARCH    LABORATORY. 


on  Pike's  Peak  (14,110  feet)  50.  An  increase  in  the  number  of 
blood  platelets  as  well  as  in  the  specific  gravity  of  the  blood  has 
been  observed.  The  following  illustrates  the  increase  in  specific 
gravity:  At  Colorado  Springs,  1.067;  after  six  months  residence  on 
Pike's  Peak,  1.073. 

THE  SEQUENCE  IN  THE  BLOOD  CHANGES  DURING  A  PERIOD  OF  RESIDENCE  AT 

HIGH  ALTITUDE. 

The  facts  so  far  given  are  those  obtained  from  the  study  of  people 
who  are  acclimatized  to  the  altitude  in  which  they  are  living.  On 
passing  from  a  low  to  a  high  altitude  some  time  is  required  to  react 
to  the  low  oxygen  of  the  new  altitude.  On  ascending  passively  to 
such  an  altitude  as  14,000  feet  it  has  been  found  that  immediately 
after  arriving  no  change  can  be  detected  in  the  number  of  red 
corpuscles  and  the  percentage  of  hemoglobin.  Just  when  the  changes 
begin  has  not  been  determined,  but  usually  within  24  hours  a  marked 
increase  in  both  will  be  present.  A  rapid  increase  in  the  number  of 
red  corpuscles  and  percentage  of  hemoglobin  occurs  during  the  first 
two  or  four  days  of  residence ;  then  follows  a  more  gradual  increase 
extending  over  three  to  five  or  more  weeks.  These  changes  are 
illustrated  in  the  following  table : 


Date. 

Havens. 

Schneider. 

Sisco. 

Hemo- 
globin. 

Corpuscles. 

Hemo- 
globin. 

Corpuscles. 

Hemo- 
globin. 

Corpuscles. 

109 
123 
126 
129 
130 
132 
135 
135 
134 
129 
132 

6,  024,  000 
6,  872,  000 
7,  024,  000 
7,  1GO,  000 
7,  292,  000 
7,  200.  000 
7,  296,  000 
7,  248,  000 
7,000,000 
6,840,000 
6,976,000 

-«  

109 
116 
115 
122 
121 
123 
121 
126 
127 
129 
129 

5,992,000 
6,472,000 
6,  400,  000 
6,800,000 
(1,848,000 
(i,  736,  000 
6,472,000 
6,616,000 
6,656,000 
6,896,000 
6,960  000 

113 
120 
125 
126 
122 
130 
133 
134 
131 
135 

6,  372,  000 
6,732,000 
6,880,000 
6,720,000 
6,624,000 
6,928,000 
7,032,000, 
7,104,000 
6,856,000 
7,  120,  000 

June  17,  Pike's  Peak  

June  18  Pike's  Peak  

June  19  Pike's  Peak  

June  20,  Pike's  Peak  

June  21,  Pike's  Peak  

June  22  Pike's  Peak            

June  24,  Pike's  Peak    

June  26,  Pike's  Peak  

June  28,  Pike's  Peak  

June  29  Pike's  Peak 

Views  differ  as  to  the  mechanism  by  which  the  changes  in  hemo- 
globin and  red  corpuscles  are  brought  about.  These  views  may  be 
conveniently  divided  into  three  main  classes:  (1)  Those  theories 
which  insist  that  the  increase  in  hemoglobin  and  red  corpuscles  is 
real  and  not  merely  relative;  two  explanations  of  the  increase  have 
been  proposed :  (a)  that  the  increase  is  due  to  increased  activity  of 
the  blood-forming  organs,  resulting  in  an  increase  in  the  hemoglobin 
and  red  corpuscles;  (b)  that  the  increase  is  due  to  a  lengthening,  of 
the  life  of  the  corpuscles.  (2)  The  concentration  theories,  according 
to  which  the  increase  in  hemoglobin  and  red  corpuscles  per  unit 
volume  is  due  to  increased  concentration  of  the  blood.  According 


MANUAL  OP  MEDICAL  RESEARCH   LABORATORY.  15 

to  this  view,  the  increase  in  both  is  only  apparent,  and  there  is  no 
increase  in  the  total  number  of  red  corpuscles  and  the  amount  of 
hemoglobin  in  the  body.  (3)  It  has  been  held  that  the  increase  in 
hemoglobin  and  corpuscles  is  due  to  unequal  distribution  of  the  red 
corpuscles.  They  are  supposed  to  be  more  numerous  in  the  blood  of 
the  capillaries  and  smaller  vessels  and  less  numerous  in  the  large 
vessels.  This  view  has  not  been  supported  experimentally  and  may 
be  considered  untenable.  It  has  further  been  supposed  that  there 
exists  in  the  body  a  reserve  or  dormant  supply  of  red  corpuscles 
which  is  drawn  upon  at  high  altitudes.  The  discussion  at  issue  seems 
to  permit  the  following,  conclusion:  The  initial  rapid  increase  in 
hemoglobin  and  red  corpuscles  is  brought  about  in  part  by  the  pass- 
ing into  the  systemic  circulation  of  a  large  number  of  red  corpuscles 
that  under  ordinary  circumstances  at  low  altitudes  are  sidetracked 
and  inactive,  and  in  part  by  a  concentration  resulting  from  a  loss  of 
fluid  from  the  blood.  The  more  gradual  increase  in  red  corpuscles 
and  hemoglobin  extending  over  several  weeks  is  brought  about  by  an 
increased  activity  of  the  blood-forming  centers,  so  that  there  results 
an  actual  increase  in  the  total  number  of  corpuscles  and  the  amount 
of  hemoglobin.  The  evidence  for  the  above  statement  can  be  briefly 
summarized.  Schneider  and  Havens  have  shown  that  abdominal 
massage  and  physical  exertion  at  low  altitudes  cause  an  increase  in 
the  number  of  red  corpuscles  and  hemoglobin  in  the  peripheral  capil- 
laries ;  while  in  men  partially  or  wholly  acclimatized  to  a  high  alti- 
tude abdominal  massage  either  does  not  change  or  lowers  the  content 
of  hemoglobin  and  red  corpuscles,  and  physical  exertion  fails  to 
cause  an  increase.  This  failure  to  obtain  an  increase  at  high  altitude 
may  be  accounted  for  on  the  assumption  that  the  need  for  oxygen 
has  called  into  permanent  circulation  the  reserve  supply  of  cor- 
puscles that  is  present  at  low  altitude.  That  an  actual  concentration 
of  the  blood  occurs  during,  the  first  few  days  of  residence  at  high 
altitude  was  proven  for  three  subjects  by  Douglas,  Haldane,  Hender- 
son, and  Schneider  during  an  investigation  made  on  Pike's  Peak. 
One  of  their  subjects  had,  after  a  few  days  of  residence,  about  a 
15  per  cent  increase  in  hemoglobin  and  a  total  blood  volume  10.8  per 
cent  less  than  at  Colorado  Springs  (altitude  6,000  feet).  Dreyer  and 
Walker,  reviewing  Abderhalden's  data,  found  that  a  little  less  than 
half  of  a  25  per  cent  increase  of  the  hemoglobin  in  rabbits,  that  Ab- 
derhalden  concluded  was  due  to  concentration,  was  actually  a  result 
of  concentration,  while  the  balance  of  it  was  to  be  explained  by  a  new 
formation  of  hemoglobin.  That  there  is  also  an  active  new  formation 
of  hemoglobin  and  red  corpuscles  is  indicated  by  several  researches. 
Thus,  Zuntz  and  co-workers  found,  on  comparing  stained  sections  of 
bone  marrow  taken  from  dogs,  one  group  of  which  had  been  kept 
at  sea  level  and  the  second  at  a  high  altitude,  that  the  latter  show 


16  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

a  decrease  in  fat  cells  and  an  increase  in  the  blood  elements.  This, 
they  concluded,  indicated  increased  activity  of  the  corpuscle-produc- 
ing centers  at  the  high  altitude.  Douglas,  Haldane,  Henderson,  and 
Schneider,  by  the  carbon-monoxide  method  of  Haldane  and  Lorraine 
Smith,  found  that  during  a  residence  of  five  weeks  on  Pike's  Peak 
(altitude  14,110  feet)  four  men  had  a  large  increase  in  the  total 
amount  of  hemoglobin  and  also  an  increase  in  the  total  volume  of 
blood.  Laquer  found  that  dog's  deprived  of  hemoglobin  of  half  of 
their  blood  supply  regenerated  it  in  about  16  days  on  Monte  Rosa, 
while  at  a  low  altitude  27  days  were  required  for  the  restoration 
after  a  similar  hemorrhage. 

It  has  been  shown  in  studies  on  Pike's  Peak  that  the  increase  in 
hemoglobin  and  red  corpuscles  for  an  individual  is  not  the  same  dur- 
ing several  trips  and  sojourns  at  that  altitude.  The  increase  occurs 
most  rapidly  when  the  subject  is  in  excellent  physical  condition.  If 
prior  to  the  ascent  his  life  has  been  sedentary  and  he  is  known  to  be 
physically  unfit  the  changes  will  be  slow  in  beginning,  and  the  in- 
crease when  followed  day  by  day  will  be  moderate  or  slight.  If,  on 
the  other  hand,  the  subject  has  taken  regular  physical  exercise  and 
is  in  excellent  condition  or  physically  fit  there  will  be  a  decided  rise 
in  both  hemoglobin  and  red  corpuscles  in  the  first  24  hours  spent  at 
the  high  altitude.  It  has  also  been  shown  that  fatigue,  induced  by 
walking  up  a  mountain,  delays  the  increase  in  hemoglobin  and  red 
corpuscles.  The  lesson  to  be  gained  from  these  observations  is  that 
physical  fitness  qualifies  the  subject  to  react  quickly  when  under  the 
influence  of  the  low  oxygen  at  high  altitudes. 

CIRCULATION    AT   HIGH   ALTITUDES. 

There  h#s  been  a  great  interest  in  the  problem  of  circulation  at 
high  altitudes.  Many  persons,  especially  those  with  weak  hearts, 
have  an  unwarranted  fear  of  high  altitudes  because  they  have  been 
informed  that  they  injure  the  heart.  The  early  studies  have  been 
of  a  fragmentary  nature,  the  observations  being  confined  wholly  to  a 
study  of  pulse  rate  and  the  systolic  blood  pressure.  It  has  recently 
been  shown  that  there  is  an  increased  rate  of  blood  flow  at  very  high 
altitudes.  This  is  a  compensatory  reaction  which  will  insure  to  the 
tissues  a  more  adequate  blood  supply.  A  more  rapid  rate  of  blood 
flow  will  raise  to  a  limited  extent  the  oxygen  pressure  in  the  blood 
passing  through  the  capillaries,  and  so  insure  better  oxidation  within 
the  tissues.  The  recent  investigations  have  included  observations 
on  the  pulse  rate,  arterial  pressures,  capillary  pressure,  and  venous 
blood  pressure.  Indirect  methods  have  also  been  employed  with  the 
hope  of  determining  the  output  of  the  heart  per  beat  as  well  as  the 
rate  of  blood  flow  through  the  lungs  and  other  tissues. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  17 

THE   PTILSE  RATE. 

Of  all  the  circulatory  changes  due  to  diminished  barometric  pres- 
sure the  acceleration  of  the  heart  rate  is  the  most  noticeable.  The 
majority  of  the  earlier  records  are  from  studies  made  of  men  who 
had  undergone  considerable  physical  exertion  in  climbing  a  moun- 
tain. The  fatigue  thus  induced  has  obscured  the  early  influence  of 
altitude.  Therefore,  in  order  to  understand  the  reaction  of  the  heart 
it  is  necessary  to  eliminate  all  extraneous  modifying  influences  such 
as  fatigue  and  cold.  Pike's  Peak  offers  an  excellent  opportunity  for 
such  Alpine  physiological  studies,  because  men  may  be  carried  up 
passively  by  railway  or  in  an  automobile. 

It  is  generally  recognized  that  at  moderately  high  altitudes,  6,000 
to  8,000  feet,  or  even  9,000  feet,  the  inhabitants  do  not  show  an  aug- 
mentation in  heart  rate.  There  is  considerable  variation  in  pulse 
rate  of  different  healthy  individuals  at  sea  level.  Thus  it  was  found 
that  athletes  in  Oxford  had  rates  which  may  be  considered  normal 
that  range  between  44  and  80.  In  a  study  of  medical  students  at 
Cambridge  the  range  was  between  47  and  90.  The  same  limits  will 
be  found  in  men  acclimated  to  the  moderate  altitudes. 

On  ascending  passively  to  a  high  altitude,  such  as  14,000  feet,  there 
is  at  first  no  noticeable  increase  in  the  rate  of  heart  beat.  What  hap- 
pens after  the  ascent  depends  on  the  condition  of  the  subject.  If  he 
has  ascended  much  beyond  what  has  been  spoken  of  as  the  critical 
altitude  line  for  the  individual  an  attack  of  mountain  sickness  is  to 
be  expected.  If  he  has  not  passed  his  critical  line,  or  only  reached  it, 
his  pulse  rate  will  continue  for  some  hours  at  the  tempo  common 
to  it  at  the  lower  altitude.  Any  exertion  will  obscure  the  altitude 
reaction;  if,  however,  he  remains  quiet,  by  the  next  morning,  even 
while  still  in  bed,  the  pulse  rate  will  be  slightly  accelerated.  Each 
successive  morning  for  three  to  five-days  the  rate  will  be  found  to  be 
somewhat  greater  than  on  the  previous  morning.  The  following 
example  illustrates  the  amount  of  change :  Thus  one  subject  who  had 
in  Colorado  Springs  (altitude  6,000  feet)  an  average  early  morning 
rate  of  53,  had  on  Pike's  Peak  the  first  morning  a  rate  of  5$;  the 
second  60 ;  the  third  63 ;  and  the  fourth  66.  In  those  who  are  influ- 
enced by  altitude  sickness  the  story  is  different.  The  heart  accel- 
erates as  the  attack  of  mountain  sickness  comes  on,  and  the  early 
morning  pulse  rate  may  have  reached  its  maximum  by  the  first 
morning.  As  the  attack  passes  off  the  heart  will  slow.  An  example 
of  this  reaction  is  found  in  the  following  subject,  who  had  in  Col- 
orado Springs  an  average  early  morning  pulse  rate  of  61.  He  became 
mountain  sick  six  hours  after  arriving  at  the  summit  of  Pike's  Peak. 
His  pulse  rate  the  next  morning  was  89,  slowing  to  80  the  second ;  to 

89119—18 2 


18  MANUAL   OF   MEDICAL  EESEAECH   LABORATORY. 

78  the  third;  and  to  72  on  the  fifth  morning.  In  men  who  undergo 
the  exertion  of  climbing  a  mountain  the  pulse  rate  reaction  is  quite 
like  that  observed  in  those  who  become  mountain  sick.  The  increase 
in  the  heart  rate  has  been  found  to  range  from  30  to  74  per  cent. 
The  amount  of  acceleration  at  high  altitudes  is  determined  to  some 
extent  by  physical  fitness.  There  will  be  less  acceleration  in  the  man 
who  is  in  the  pink  of  condition,  while  the  augmentation  is  great  in 
those  who  had  been  leading  a  sedentary  life  and  are  physically  below 
par.  The  daily  mean  pulse  rate  for  men  at  high  altitudes  shows 
approximately  the  same  proportionate  increase  as  the  early  morning 
pulse  rate  does  when  compared  with  rates  experienced  at  lower  alti- 
tudes. The  influence  of  posture  upon  pulse  rate  has  been  investi- 
gated, and  it  has  been  established  that  the  heart  is  not  necessarily 
more  irritable  to  changes  in  body  position  at  high  than  at  low  alti- 
tudes. In  general  it  may  be  said  that  the  heart  works  at  an  increased 
rate  in  all  postures  at  the  high  altitude.  The  amount  of  increase  in 
the  pulse  rate  differs  with  individuals.  Some  men  will  show  at  the 
high  altitude,  such  as  14,000  feet,  an  acceleration  of  only  a  few  beats 
over  the  low  altitude  rate,  while  others  show  an  increase  of  10  or 
more  beats  per  minute. 

'During  a  sojourn  at  a  high  altitude  the  pulse  rate  may  show  a 
gradual  daily  increase  for  a  period  of  one  or  two  weeks,  ordinarily 
not  more  than  one  week.  With  longer  residence  there  is  a  tendency 
to  return  toward  the  low  altitude  rate.  It  appears  that  the  slowing 
of  the  heart  takes  place  as  other  adaptive  changes  reach  their  maxi- 
mum efficiency.  Barely,  does  the  pulse  rate  return  completely  to  the 
normal  rate  of  the  low  altitude. 

ARTERIAL   PRESSURES. 

In  recent  years  stress  has  been  laid  on  blood  pressure  findings  at 
high  altitudes,  the  value  of  which  has  undoubtedly  been  overesti- 
mated. Just  what  normal  blood  pressures  are  at  sea  level  is  a  matter 
concerning  which  there  is  the  widest  diversity  of  opinion.  Janeway 
states  that  "in  the  great  majority  of  young  males,  100  to  130  mm. 
will  be'  found  ",  and  names  the  normal  diastolic  pressure  as  from  65 
to  110.  Faught  states  that  120  may  be  taken  as  the  normal  systolic 
pressure  in  the  male  at  the  age  of  20  and  adds  1  millimeter  for  every 
additional  2  years  of  life.  He  believes  that  the  question  as  to  what 
variations  from  this  are  normal  can  not  be  definitely  answered,  but 
suggests  17  mm.  above  or  below,  or  a  total  variation  of  34.  The 
most  satisfactory  data  on  blood  pressures,  as  far  as  the  interpreta- 
tion of  altitude  effect  is  concerned,  is  that  obtained  from  observations 
made  upon  the  same  men  at  both  a  low  and  a  high  altitude.  Such 
comparisons  have  been  made  on  Pike's  Peak.  Data,  accumulated 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  19 

during  a  period  of  more  than  5  years  in  the  laboratory  at  Colorado 
College  in  Colorado  Springs,  show  that  at  an  altitude  of  6,000  feet 
the  systolic  pressure  is  in  the  majority  of  young  men  less  than 
120  mm.  and  falls  within  the  range  given  by  Janeway.  The  dias- 
tolic  pressure  likewise  corresponds  to  that  observed  in  young  men 
at  sea  level.  We  may  conclude  then  that  at  moderate  altitude,  nor- 
mal healthy  young  men  show  the  same  ran^e  and  distribution  of 
pressures  as  do  young  men  at  sea  level. 

Many  physicians  still  believe  that  at  high  altitudes,  such  as  14,000 
feet,  the  blood  pressure  increases  simultaneously  with  the  decrease 
in  atmospheric  pressure,  and  they  conclude  that  this  increase  means 
injury,'  especially  to  the  weakened  heart.  The  investigations  of 
more  recent  years  show  that  this  opinion  is  untenable.  The  observa- 
tions on  Pike's  Peak  which  extend  over  a  number  of  years  and  which 
were  made  upon  men  who  ascended  the  mountain  passively  show 
that  in  those  who  react  well  to  the  altitude  the  changes  were  sur- 
prisingly slight,  in  fact,  they  were  so  slight  that  they  fall  for  the 
most  part  within  the  errors  of  observations.  Schneider  and  Sisco 
concluded  that  for  many,  and  very  likely  the  vast  majority  of  healthy 
men,  an  altitude  of  14,000  feet  does  not  influence  the  arterial  blood 
pressures.  In  a  certain  but  as  yet  undetermined  percentage  of  men 
this  altitude  will  cause  a  demonstrable  fall,  arid  in  exceptional  men, 
particularly  those  who  do  not  react  well  to  the  high  altitude,  will 
bring  about  a  rise  in  the  arterial  pressures. 

During  an  attack  of  mountain  sickness  there  will  be  manifested  a 
disturbance  in  circulation,  as  shown  by  the  definite  rise  in  the  arterial 
pressures.  Thus  in  one  subject  the  following  changes  in  pressure 
were  noted  during  and  after  an  attack  of  mountain  sickness:  In 
Colorado  Springs,  6,000  feet,  he  averaged  in  systolic  pressure  118. 
and  in  diastolic  85.  On  going  to  the  summit  of  Pike's  Peak  he  was 
ill  with  mountain  sickness  the  first  three  days,  during  which  time 
his  systolic  pressure  averaged  129,  and  the  diastolic  pressure  91. 
However,  by  the  morning  of  the  fourth  day  he  was  decidedly  better,  • 
in  fact,  had  recovered,  and  during  the  next  three  days  his  systolic 
pressure  averaged  116,  and  the  diastolic  84.  The  fear  of  high  alti- 
tudes undoubtedly  is  a  result  of  over-emphasis  of  the  circulatory  con- 
ditions observed  during  the  early  days  spent  at  a  high  altitude  when 
the  organism  has  not  as  yet  accommodated  itself  to  the  new  condi- 
tions of  environment.  Certainly  after  adjustment  the  blood  pres- 
sures do  not  show  an  important  change. 

VENOUS  BLOOD  PRESSURE. 

Venous  pressures  have  not  received  the  same  amount  of  attention 
at  either  high  or  low  altitudes  as  have  the  arterial  pressures.  It  is 
only  in  recent  years  that  satisfactory  methods  of  observing  venous 


20  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

pressure  have  been  available.  Hooker  in  Baltimore  finds  that  in 
healthy  men  the  venous  pressure  varies  or  ranges  between  2  and 
16  centimeters  of  water.  Schneider  and  Sisco  found  the  same  pres- 
sures may  be  considered  as  normal  on  healthy  young  men  at  an  alti- 
tude of  6,000  feet.  On  Pike's  Peak  they  find  a  marked  fall  of  between 
20  and  87  per  cent  in  the  venous  pressure  of  healthy  young  men. 
The  changes  in  venous  ^pressure  occurred  slowly,  in  fact,  in  some  of 
their  subjects  the  pressure  was  somewhat  higher  during  the  first  half 
day  spent  at  the  higher  altitude.  While  the  venous  pressure  was 
shown  to  fall,  they  found  the  venous  supply  of  blood  and  the  venous 
pressure  remained  sufficient  at  the  altitude  to  give  a  maximum  effi- 
ciency of  heartbeat. 

CAPILLARY  BLOOD  PRESSURE. 

Lombard  has  shown  for  low  altitudes  that  the  most  compressible 
capillaries  disappear  at  a  pressure  between  15  and  25  millimeters 
of  mercury.  The  average  capillary  between  35  and  45  millimeters, 
and  the  most  resisting  capillaries  between  60  and  70  millimeters. 
On  Pike's  Peak  the  capillary  pressures  were  in  some  men  slightly 
lower  than  when  at  an  altitude  of  6,000  feet,  while  in  others  the 
capillary  pressures  were  unaffected  by  altitude. 

It  has  been  frequently  claimed  that  bleeding  from  the  nose,  lips, 
gums,  lungs,  and  stomach  is  a  common  experience  at  high  altitudes 
and  this  has  been  attributed  to  increased  capillary  pressure.  The 
above  observations  show  this  conclusion  to  be  incorrect.  Among  the 
thousands  of  people  that  ascend  Pike's  Peak  every  summer  there  oc- 
cur only  a  few  cases  of  hemorrhage  and  these  are  of  the  nose  only. 
Such  cases  are  so  rare  that  doubt  would  be  thrown  on  the  usual  ex- 
planation, even  in  the  absence  of  positive  proof  that  capillary  pres- 
sure is  not  increased  with  altitude. 

THE  OUTPUT  OF  THE  HEART  AND  THE  RATE  OF  BLOOD  FLOW. 

Attempts  made  to  determine  the  output  of  blood  per  beat  from  the 
heart  have  not  tyeen  very  successful.  By  use  of  the  recoil  method 
of  Yandell  Henderson  the  mass  movement  of  the  blood  has  been 
studied  on  Pike's  Peak.  The  observations  indicate  that  the  output 
of  the  heart  is  either  the  same  as  at  low  altitude  or  may  be  slightly 
less.  It  is  assumed  that  the  pulse  pressure  is  an  index  of  the  heart 
output  per  beat.  Since  it  has  been  shown  that  the  pulse  pressure  is 
the  same  at  the  high  and  low  altitudes  for  particular  subjects  under 
observation  we  may  be  permitted  to  conclude  that  the  output  of  the 
heart  is  unchanged  with  altitude.  If  the  pulse  rate  be  multiplied  by 
the  pulse  pressure  and  the  product  be  taken  as  a  relative  measure  of 
the  volume  of  the  blood  stream  per  minute,  a  marked  increase  in  the 
circulation  rate  is  indicated  for  high  altitudes. 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  21 

That  the  rate  of  blood  flow  is  increased  with  altitude  has  been 
shown  by  two  researches.  Schneider  and  Sisco  used  Stewart's  calo- 
rimeters to  determine  the  rate  of  the  blood  flow  through  the  hands. 
The  method  determines  the  amount  of  heat  given  off  by  the  resting 
hand  in  a  given  time  and  indirectly  the  temperatures  of  the  arterial 
and  venous  blood.  With  these  data  it  is  possible  to  calculate  how 
much  blood  has  passed  through  the  hand  in  order  that  it  might  give 
off  a  determined  amount  of  heat.  By  this  method  the  blood  flow 
through  100  c.  c.  of  hand  volume  was  shown  to  be  from  30  to  70  per 
cent  greater,  in  six  men  studied,  on  the  summit  of  Pike's  Peak  than 
in  Colorado  Springs.  Kuhn,  on  Monte  Rosa,  also  has  demonstrated, 
by  calculations  made  from  determinations  of  the  oxygen  capacity  of 
the  blood,  the  total  oxygen  consumption  and  the  pulse  rate,  that  the 
per  minute  output  of  the  heart  is  increased  at  that  high  altitude. 

WHAT  CAUSES  THE  CIRCULATORY  CHANGES  REPORTED  AND  THE  INCREASED 

RATE    IN    FLOW? 

All  adaptive  changes  occurring  at  high  altitudes  seem  to  be  for  the 
purpose  of  supplying  a  more  adequate  supply  of  oxygen  for  the 
tissues.  If,  therefore,  oxygen  want  is  the  cause  of  the  observed  in- 
crease in  the  flow  of  the  blood,  it  is  to  be  expected  that  the  inhalation 
of  pure  oxygen  while  at  the  high  akitude  may  so  benefit  the  body 
as  to  retard  the  heart  and  diminish  the  rate  of  the  blood  flow. 
Schneider  and  Sisco  found  that  the  breathing  of  an  oxygen-rich  mix- 
ture while  on  Pike's  Peak  slowed  the  heart  appreciably  and  dimin- 
ished the  rate  of  the  blood  flow  through  the  hands;  from  which  we 
may  conclude  that  lack  of  oxygen  calls  forth  certain  definite  circu- 
latory responses  in  men  for  the  purpose  of  increasing  the  rate  of 
blood  flow,  in  order  that  the  oxygen  pressure  may  be  sufficient  to  fur- 
nish the  tissues  with  the  oxygen  needed  as  the  blood  passes  through 
the  capillaries. 

THE    EFFECTS    OF    PHYSICAL    EXERTION    ON    THE    PULSE    RATE    AND    THE 
BLOOD  PRESSURES  AT  HIGH  ALTITUDE. 

The  normal  circulatory  conditions  for  the  majority  of  men  at 
high  altitudes  are  an  increased  rate  of  heart  beat  and  an  unchanged, 
or  slightly  lowered,  arterial  pressure,  and  a  lowered  venous  pres- 
sure. All  investigators  have  found  that  a  more  marked  increase  in 
the  pulse  rate  occurs  during  work  at  a  high  than  results  with  the' 
same  exertion  at  a  low  altitude.  Just  what  height  must  be  reached 
before  altitude  accelerates  the  exercise  pulse  rate  has  not  been  defi- 
nitely determined,  but  the  inhabitants  at  6,000  feet  show  no  notice- 
able exercise  altitude  effect.  Observations  on  the  after-effects  of 
walking  for  15  minutes  at  the  rate  of  3  and  4  miles  per  hour,  show 


22  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

clearly  that  physical  exertion  accelerates  the  heart  more  at  a  high 
than  at  a  low  altitude  and  that  the  influence  is  disproportionately 
increased  as  the  amount  of  work  is  increased.  The  effect  of  the 
lowered  barometric  pressure  is  manifest  not  only  in  the  greater  ac- 
celeration of  the  heart,  but  in  the  great  extention  in  the  time  required 
for  the  rate  to  return  to  the  normal  after  work  has  ceased.  Further- 
more, these  altitude  reactions  are  greatest  during  the  first  days  and 
become  less  as  the  individual  becomes  acclimated.  The  arterial  pres- 
sures will  be  higher  after  a  given  rate  of  walking  at  a  high  altitude 
than  after  the  same  amount  of  work  at  a  lower  altitude.  Here  like- 
wise the  greater  the  exertion  the  more  pronounced  is  the  influence  of 
lowered  barometric  pressure.  In  physically  fit  men  the  effect  of  al- 
titude is  much  less.  The  facts  show  that  the  heart  and  the  blood 
vessels  undergo  a  greater  strain  under  exertion  at  the  high  than 
is  experienced  for  the  same  form  of  exercise  at  low  altitudes.  The 
excessive  response  of  the  circulatory  mechanism  during  and  immedi- 
ately following  physical  work  is  greatest  during  the  first  days;  and 
descreases,  particularly  for  moderate  exertion,  as  the  bodily  changes 
of  the  acclimatization  progress.  For  persons  in  excellent  physical 
condition  and  who  have  reacted  well  to  the  altitude  the  changes  of  the 
acclimatization  will  permit  of  moderate  exertion  without  a  lowered 
barometric  pressure  manifesting  itself  by  the  more  pronounced  ac- 
celeration of  heart  rate  and  increased  blood  pressure.  The  evidence 
at  hand  makes  it  probable  that  in  vigorous  work,  even  in  those  who 
are  best  adapted  to  the  high  altitudes,  one  will  continue  to  get  a 
more  pronounced  reaction  than  would  occur  at  a  low  altitude.  In 
order  that  the  effects  of  acclimatization  may  be  better  understood 
the  following  examples  of  the  circulatory  effects  of  altitude  are 
given:  Walking  for  15  minutes  at  the  rate  of  3  miles  an  hour  in 
Colorado  Springs  one  subject  had  the  following  changes:  An  in- 
crease of  11  beats  in  pulse  rate  and  no  change  in  systolic  and  diastolic 
pressures.  During  the  first  day  spent  on  Pike's  Peak  a  similar  walk 
accelerated  the  pulse  34  beats,  caused  a  rise  in  the  systolic  pressure 
of  28  mm.,  and  in  the  diastolic  4  mm.  On  the  fourth  day  of  resi- 
dence this  amount  of  work  accelerated  the  pulse  only  24  beats,  in- 
creased the  systolic  pressure  8  mm.,  and  did  not  affect  the  diastolic 
pressure.  This  same  subject,  walking  at  the  rate  of  4  miles  per  hour 
for  15  minutes  in  Colorado  Springs  had  the  following  reactions: 
Average  increase  in  pulse,  24  beats;  systolic  pressure,  6  mm.;  and 
diastolic  pressure,  1  mm.  The  first  day  spent  on  Pike's  Peak,  this 
amount  of  exercise  accelerated  to  pulse  61  beats,  systolic  pressure 
44  mm.,  and  diastolic  pressure  7  mm.  On  the  fourth  day  the  pulse 
increased  54  beats,  systolic  23  mm.,  and  diastolic  4  mm.  These 
observations  suggest  that  it  would  be  best  to  avoid  physical  work 
during  the  first  days  spent  at  very  high  altitudes. 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  23 

It  is  to  be  expected  that  living  at  a  high  altitude,  especially  when 
much  physical  work  is  done,  will  increase  the  weight  of  the  heart, 
for  all  muscular  exertion  tends  to  increase  the  weight  of  the  heart, 
and  the  result  of  the  work  at  high  altitudes  would  accentuate  the 
tendency.  Strohl  compared  the  heart  of  Alpine  snow  birds  living  at 
altitudes  ranging  from  6,700  to  10,000  with  the  Moor  snow  bird, 
which  is  not  found  above  2,000  feet,  and  found  that  the  average 
weight  of  the  heart  of  the  Alpine  snow  bird  was  about  46  per  cent 
heavier  than  that  of  the  Moor  bird.  The  hypertrophy  of  the  right 
was  greater  than  that  of  the  left  ventricle.  He  made  one  observation 
of  considerable  interest,  in  which  he  found  that  the  heart  of  a 
young  Alpine  snow  bird  one  and  a  half  months  old  had  the  same 
proportions  in  weight  as  that  of  the  Moor  snow  bird,  which  suggests 
that  the  differences  ordinarily  observed  at  the  two  altitudes  are  due 
to  the  greater  circulatory  reactions  called  forth  during  muscular 
work  at  the  high  altitude. 

RESPIRATION    AT  HIGH   ALTITUDE. 

It  has  been  known  since  the  researches  by  Haldane  and  pupils 
that  the  volume  of  fresh  air  taken  into  the  lungs  per  minute  during 
rest  is  so  regulated  as  to  keep  the  partial  pressure  of  carbon  dioxide 
in  the  alveolar  air  practically  constant  for  the  individual.  There- 
fore the  carbon  dioxide  content  of  the  alveolar  air  is  taken  as  an 
index  of  lung  ventilation.  The  breathing,  however,  is  dependent  on 
the  integrity  of  a  very  small  area,  the  respiratory  center,  of  the  brain 
in  the  medulla  oblongata.  The  reaction  of  this  center  is  regarded  as 
automatic,  and  any  interference  with  its  supply  of  properly  aerated 
blood  causes  greatly  increased  activity  and  thereby  increased  breath- 
ing. Carbon  dioxide  in  the  blood  is  the  stimulant  which  excites  this 
nervous  center  of  our  respiratory  mechanism  and  maintains  its 
regular  action.  There  is  no  doubt  that  slight  changes  in  carbon  di- 
oxide in  the  blood  affect  the  respiratory  center.  The  effects  of  these 
changes  are  rapid  and  marked  when  in  laboratory  experiments  with 
animals  all  the  nervous  connections  between  the  lungs  and  the 
respiratory  center  are  severed.  A  decrease  in  the  amount  of  oxygen 
in  the  blood  will  also  affect  the  respiratory  center.  It  is  generally 
held  that  the  amount  of  oxygen  must  be  markedly  lowered  before  the 
respiratory  center  begins  to  be  stimulated  by  the  decrease  in  oxygen. 
For  our  present  purposes,  the  explanation  of  the  breathing  changes 
at  high  altitudes,  attention  may  be  centered  on  the  carbon  dioxide 
content  of  the  blood  and  in  the  alveoli  of  the  lungs.  Both  the  per- 
centage of  oxygen  and  that  of  carbon  dioxide  are  very  constant  in 
the  alveolar  air  in  spite  of  great  changes  in  the  amount  of  oxygen 
consumed  and  carbon  dioxide  given  off  by  the  body.  Since  the 
volume  of  fresh  air  taken  into  the  lungs  per  minute  is  so  regulatecl 


24  MANUAL  OF   MEDICAL  EESEAKCH   LABOEATOEY. 

as  to  keep  the  partial  pressure  of  carbon  dioxide  in  the  alveolar  air 
practically  constant  for  each  individual  (at  about  40  mm.  for  adult 
men  at  sea  level),  the  alveolar  ventilation  must  vary  according  to  the 
mass  of  carbon  dioxide  given  off.  Even  during  muscular  work  this 
rule  holds  approximately  true  under  ordinary  conditions.  A  diminu- 
tion in  the  alveolar  carbon  dioxide  pressure  has  been  found  to  indi- 
cate an  increase  in  the  lung  ventilation,  while  an  increase  in  carbon 
dioxide  means  lessened  ventilation  and  a  reduction  in  alveolar 
oxygen. 

The  ventilation  of  the  lungs  for  people  dwelling  at  high  altitudes 
is  greater  than  that  of  mankind  living  at  sea  level.  On  going  from 
sea  level  to  an  altitude  of  6,000  feet,  with  a  fall  of  about  145  mm. 
from  normal  in  barometric  pressure,  the  alveolar  carbon  dioxide  pres- 
sure is  lowered  about  4  mm. ;  and  on  further  ascending  to  the  summit 
of  Pike's  Peak  (14,110  feet)  with  an  added  decrease  of  about  160 
mm.  in  barometric  pressure,  the  alveolar  carbon  dioxide  pressure 
falls  on  an  average  about  10  mm.  more.  This  is  a  little  more  than  a 
30  per  cent  decrease  and  indicates  a  corresponding  increase  in  the 
breathing.  The.  full  extent  of  the  fall  takes  about  two  weeks  to  de- 
velop, and  thereafter  the  carbon  dioxide  pressure  will  remain  prac- 
tically steady. 

If  the  same  alveolar  carbon  dioxide  pressure  were  to  be  maintained 
on  Pike's  Peak  with  a  barometric  'pressure  of  about  457  mm.  that  is 
normal  at  sea  level,  there  would  be  a  marked  shortage  of  oxygen.  This 
would  be  true,  because  a  deficiency  of  oxygen  in  the  alveolar  air 
always  .runs  parallel  to  the  excess  in  carbon  dioxide.  If  the  carbon 
dioxide  pressure  remained  at  40  mm.  while  the  atmospheric  pressure 
had  fallen  from  760  to  457  mm.,  it  would  amount  to  a  relative  in- 
crease of  about  27  per  cent  in  the  carbon  dioxide  and  a  similar 
decrease  in  oxygen.  The  partial  pressure  of  oxygen  in  the  alveolar 
air  would  therefore  be  about  50  mm.  lower  than  in  the  inspired  air. 
Allowing  for  the  pressure  of  aqueous  vapor  at  body  temperature,  it 
is  found  that  the  pressure  of  oxygen  in  the  lungs  at  the  altitude  of 
Pike's  Peak  would  be  36  mm.  This  is  an  oxygen  pressure  which 
would  be  found  if  dry  alveolar  air  contained  only  5  per  cent  of 
oxygen  at  normal  atmospheric  pressure,  and  it  is  known  that  marked 
symptoms  of  want  of  oxygen  are  ordinarily  produced  under  such 
conditions.  Parallel  with  the  fall  of  about  13  mm.  in  the  alveolar 
carbon  dioxide  pressure  on  Pike's  Peak  there  occurs  a  rise  in  the 
alveolar  oxygen  pressure  of  a  little  more  than  16  mm.  so  that  the 
alveolar  oxygen  pressure  at  that  altitude  is  about  52  mm.  This  rise  in 
the  oxygen  above  what  might  be  expected  when  carbon  dioxide  re- 
mains unchanged  is  due  to  increased  breathing. 

On  going  to  a  very  high  altitude  the  breathing  is  increased  at 
cnce  and  the  alveolar  carbon  dioxide  pressure  falls  correspondingly, 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


25 


but  if  the  altitude  is  only  very  moderate  there  is  at  first  no  effect  on 
the  breathing.  After  some  days,  however,  it  will  be  found  that  the 
alveolar  carbon  dioxide  pressure  has  fallen,  indicating  that  the  breath- 
ing is  deeper.  The  fall  reaches  a  certain  amount  and  the  breathing 
a  certain  depth,  depending  on  the  altitude,  and  then  ceases.  Studies 
on  persons  residing  permanently  at  different  altitudes  show  that 
there  is  a  progressive  decrease  in  the  alveolar  carbon  dioxide  pres- 
sure corresponding  to  increase  in  altitude.  For  every  fall  of  100 
mm.  of  barometric  pressure  there  is  approximately  a  fall  of  4.2  mm. 
in  the  pressure  in  the  alveolar  carbon  dioxide.  There  is  likewise  a 
progressive  fall  in  the  oxygen  pressure,  but  this  does  not  follow 
exactly  the  same  ratio  as  the  carbon  dioxide  changes.  The  following 
illustrates  alveolar  air  altitude  changes: 


Barometer. 

Carbon 
dioxide 
pressure. 

Oxygen 
pressure. 

Sea-level            

760 

Mm. 
40 

Mm. 
100 

6,000  feet           

615 

36 

78 

14,100  feet  -  

458 

27 

53 

24,600  feet            

312 

21 

33 

That  the  diminution  in  carbon  dioxide  is  a  response  to  the  dimin- 
ished oxygen  pressure  there  can  be  no  doubt.  If  the  barometric  pres- 
sure is  kept  steady  and  the  oxygen  pressure  is  diminished  by  lower- 
ing the  percentage  of  oxygen,  the  results  are  precisely  the  same  as 
those  obtained  with  changes  in  altitude. 

Since  the  content  of  carbon  dioxide  and  oxygen  in  the  lung  alveoli 
give  an  index  of  the  total  ventilation*  of  the  lungs  in  breathing,  fre- 
quent chemical  analyses  of  the  alveolar  air  during  and  after  an  ascent 
will  indicate  how  much  the  breathing  is  increasing.  As  stated  above, 
the  breathing  responds  at  once  as  an  ascent  is  made,  but  the  changes 
are  not  completed  for  several  weeks.  The  following  data  will  illus- 
trate the  rate  of  change :  . 


Percentage  of  gases 
in  alveolar  air. 

Partial  pressure  of 
gases  in  alveolar  air. 

CO2. 

Oi. 

CO2. 

02. 

Sea-level  

5.55 

6.54 
7.8 

14.08 
12.94 

39.6 
37.3 
32  2 

100.4 
73.8 

Colorado  Springs  

Pike's  Peak  (14,110  feet)  

40  minutes  after  arrival  

7.52 
7.41 
7.21 

11.38 
11.26 

31.1 
30.7 

47.1 
46.6 

Second  day  

Fourth  day  

Seventh  dav  ,-  

7.21 
6.63 

11.98 
13.08 

29.6 
27.4 

49.0 
54.0 

Twenty-eighth  day  

26  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

In  physiology  it  is  found  that  the  action  of  gases  within  the  body  is 
determined  by  the  pressure  and  not  by  the  percentage  of  gas.  The 
above  table  shows  that  the  percentage  of  alveolar  carbon  dioxide 
rises  with  the  altitude,  but  as  its  partial  pressure  is  determined  by  the 
barometric  pressure  we  find  that  there  is  a  fall  in  the  alveolar  carbon 
dioxide  partial  pressure  as  altitude  increases.  As  the  partial  pressure 
of  carbon  dioxide  in  the  alveolar  air  is  about  a  third  less  (about  27 
mm.  as  compared  with  40  mm.)  on  Pike's  Peak  than  at  sea  level,  it  is 
evident  that  the  alveolar  ventilation  during  rest  for  an  equal  produc- 
tion of  carbon  dioxide  is  about  30  per  cent  greater  than  on  Pike's 
Peak.  Actual  measurements  show  that  the  volume  of  air  breathed 
by  a  subject  on  Pike's  Peak  is  27  per  cent  greater  during  rest  in  bed, 
about  31  per  cent  greater  when  standing  at  rest,  about  50  per  cent 
greater  when  walking  at  the  rate  of  4^  miles  per  hour,  and  100  per 
cent  greater  during  more  severe  exertion  than  for  similar  experiences 
at  sea  level.  An  increase  of  30  to  50  per  cent  in  the  air  breathed  when 
the  subject  is  at  rest  is  not  noticeable  subjectively.  During  hard 
work,  on  the  other  hand,  an  increase  of  50  per  cent  in  alveolar  venti- 
lation is  very  noticeable  since  panting  becomes  excessive  with  a  good 
deal  of  muscular  work.  During  hard  work,  'even  at  sea  level,  the  depth 
of  breathing  is  about  maximal.  Hence  the  increased  alveolar  ventila- 
tion at  a  high  altitude  during  exertion  implies  a  corresponding  in- 
crease in  the  frequency  of  breach,  with  a  corresponding  increased 
sense  of  effort.  It  is  clear,  therefore,  that  at  the  high  altitudes,  such 
as  14,000  feet,  there  is  excessive  hyperpnea  on  exertion.  The 
hyperpnea  is  probably  about  three  times  greater  than  would  be  the 
case  with  a  corresponding  exertion  at  sea  level.  Walking  at  the  rate 
of  4  miles  an  hour  at  sea  level  Vould  cause  no  respiratory  inconven- 
ience, but  the  same  work  at  14,000  feet  causes  extreme  and  urgent 
hyperpnea.  Excessive  hyperpnea  on  exertion  persists  at  14,000  feet 
during  the  entire  sojourn,  but  it  becomes  less  marked  after  the  first 
day  or  two. 

During  inaction  the  breathing  at  high  altitude  is  ordinarily  modi- 
fied only  in  depth.  The  rate  of  breathing  at  sea  level  varies  normally 
between  14  and  18  breaths  per  minute.  In  many  men  "this  rate  also 
continues  at  an  altitude  of  41,000  feet.  During  exertion  the  rate 
must  increase  since  at  sea  level  for  a  given  exercise  the  breathing  is 
often  maximal.  It  follows,  therefore,  that  the  same  exertion  at  the 
high  altitude,  if  it  increases  the  total  ventilation  of  the  lungs,  can 
only  do  so  by  increasing  the  rate  of  breathing.  The  following  ob- 
servations made  on  Pike's  Peak  clearly  prove  the  above  statement: 
The  subject  had  breathed  when  in  bed  at  sea  level  at  the  rate  of  16.8 
breaths  per  minute,  when  on  Pike's  Peak  17.3;  on  standing  at  sea 
level  17  breaths  per  minute,  on  Pike's  Peak  20 ;  walking  at  the  rate  of 
4  miles  per  hour  at  sea  level  17.2  breaths  per  minute,  on  Pike's  Peak 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  27 

29;  and  at  the  rate  of  5  miles  per  hour  at  sea  level  20  breaths  per 
minute,  on  Pike's  Peak  36. 

To  explain  the  fall  in  alveolar  carbon  dioxide  pressure  and  the 
increased  ventilation  of  the  lungs  at  high  altitudes  it  is  necessary  to 
consider  the  changes  that  occur  in  the  blood.  Greater  stress  was  laid 
by  Mosso  upon  the  diminished  carbon  dioxide  in  the  breath,  not  be- 
cause its  diminution  is  of  any  importance  in  the  breathing,  but  be- 
cause this  is  the  reflection  of  a  lowered  carbon  dioxide  pressure  in 
the  body  generally.  Want  of  carbon  dioxide  would,  other  things 
being  equal,  affect  the  affinity  of  the  blood  for  oxygen.  Decreased 
carbon  dioxide  alone  in  the  blood  would  increase  the  affinity  of  the 
blood  for  oxygen.  However,  with  the  increase  in  altitude  it  is  found 
that  the  affinitj*  of  the  blood  for  oxygen  remains  approximately  un- 
altered in  spite  of  the  lower  carbon  dioxide  tension.  This  suggests 
that  as  one  ascends  the  carbon  dioxide  in  the  blood  is  replaced  by 
something  else  which  produces  an  equal  effect  on  the  affinity  of  the 
hemoglobin  for  oxygen.  A  study  of  the  dissociation  curve  of -the 
blood  made  by  Barcroft  at  various  altitudes  indicates  that  there  is 
an  increase  in  the  acid  radicals,  or  a  decrease  in  the  bases  of  the 
blood.  The  higher  the  altitude  reached  the  more  marked  is  the 
acidosis,  but  at  any  given  altitude  the  acidosis  and  the  diminution 
of  carbon  dioxide  so  nearly  balance  each  other  that  the  reaction  of 
the  blood  remains  practically  constant.  Only  a  very  careful  study 
has  been  able  to  show  that  the  increase  of  acidity  is  slightly  in  excess 
of  the  loss  of  carbon  dioxide.  This  would  lower  the  affinity  of  the 
blood  for  oxygen  very  slightly;  but  at  the  same  time  the  change 
would  be  sufficient  to  give  the  increased  stimulation  to  the  respiratory 
center,  which  would  account  for  the  increased  ventilation  of  the 
lungs.  What  acid  is  responsible  for  the  acidosis  in  the  blood  at  high 
altitudes  has  not  yet  been  ascertained.  It  was  once  thought  that 
lurtic  acid  appeared  in  the  blood  with  the  acclimatization  to  high 
altitude,  but  this  is  not  maintained  at  present.  It  may  be  that  there". 
is  no  increase  of  acid  at  all,  but,  rather,  a  diminution  in  the  amount 
of  alkali  present.  The  fact  that  the  alkalinity  of  the  blood  is 
diminished  at  high  altitudes  was  first  demonstrated  by  Galeoti  in 
1903.  At  that  time  it  was  already  known  that  lactic  acid  is  pro- 
duced by  an  excessive  muscular  exertion,  as  a  consequence,  no  doubt, 
of  a  lack  of  oxygen  in  the  active  muscles,  and  this  suggested  that 
lactic  acid  is  formed  when  the  organism  experiences  the  oxygen 
want  at  high  altitudes.  But  the  excess  of  lactic  acid  formed  during 
muscular  exertion  disappears  again  within  an  hour,  together  with  its 
effect  on  the  alveolar  carbon  dioxide  pressure.  If  the  diminished 
alkali  of  blood  at  high  altitudes  were  simply  due  to  lactic  acid 
formed  in  excess,  we  should  similarly  expect  this  diminished  alka- 


28  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

linity  to  'disappear  and  appear  rapidly,  and  would  expect  similar 
marked  variation  in  the  alveolar  carbon  dioxide  pressure.  The  in- 
crease in  acid  in  the  blood  and  the  lowering  of  the  alveolar  carbon 
dioxide,  however,  require  days  to  develop.  Vezar  has  shown  that 
oxygen  want  increases  the  activity  of  the  kidneys,  which  suggests 
that  oxygen  want  so  affects  the  kidney  that  it  excretes  alkali  more 
freely.  It  certainly  looks  as  if  the  blood  and  the  breathing  changes 
were  due  to  some  adaptive  alteration  in  the  regulation  of  blood 
alkalinity.  "  The  fixed  alkalinity  of  the  body  as  a  whole,  including 
the  blood,  is  evidently  regulated  normally  by  the  action  of  the 
kidneys,  although  the  liver,  by  varying  the  amount  of  ammonia  in 
the  blood,  may  also  contribute  to  the  regulation.  A  slight  and 
gradual  adaptive  alteration  in  what  one  may  call  the  exciting 
threshold  of  alkalinity  for  the  kidneys  would  explain  the  reduced 
fixed  alkalinity  of  the  blood  in  acclimatized  persons."  The  above 
observations,  if  correct,  indicate  that  there  is  a  loss  of  reserve  alka- 
linity among  the  inhabitants  of  high  altitudes  which  may  place  the 
body  at  a  disadvantage  in  certain  pathological  conditions. 

OTHER  ALTITUDE  RESPIRATORY  OBSERVATIONS. 

Periodic  breathing  is  frequently  observed  among  newcomers  at 
very  high  altitudes— the  type  varying  in  different  persons.  It  may 
occur  in  groups  of  three  or  four  breaths,  each  succeeding  breath  being 
deeper  than  the  preceding  one  and  each  group  then  followed  by  a 
pause  in  breathing;  or  there  may  be  no  pause,  the  breaths  occurring 
in  groups  of  6  to  10  in  which  there  is  a  gradual  increase  in  depth  to 
the  mid-point  and  then  a  gradual  decrease.  The  periodic  breathing 
often  is  initiated  by  muscular  exertion  and  may  be  started  at  any 
time  by  a  few  forced  breaths  or  by  holding  the  breath  a  few  seconds. 
No  doubt  the  spontaneous  periodic  breathing  met  with  at  the  high 
altitudes  depends  upon  want  of  oxygen  in  that  it  has  been  shown 
that  it  may  be  abolished  by  the  administration  of  pure  oxygen.  Peri- 
odic breathing  disappears  in  the  majority  of  men  as  they  become 
acclimated  to  the  altitude. 

The  ability  to  hold  the  breath  is  decreased  at  high  altitudes.  It 
has  been  found  that  when  first  arriving  at  14,000  feet  men  may  be 
able  to  hold  the  breath  almost  as  long  as  at  a  low  altitude.  Day 
after  day,  for  some  time,  it  will  be  found  that  the  voluntary  effort 
of  holding  the  breath  becomes  greater  and  that  the  period  of  holding 
grows  shorter.  No  doubt  the  ability  to  hold  the  breath  decreases  as 
the  acidosis  of  the  blood  increases. 

It  is  a  popular  belief  that  high  altitudes  increase  the  size  of  the 
chest  and  the  vital  capacity.  Humboldt,  in  1799,  claimed  to  have 
observed  this  increase  in  people  of  the  Andes ;  and  Williams  noted 
the  same  result  after  residence  in  a  high  mountain  resort.  With 


MANUAL  OF   MEDICAL  RESEARCH  LABORATORY.  29 

these  exceptions  all  observers  agree  that  for  the  majority  of  persons 
the  low  atmospheric  pressure  alone  does  not  increase  the  vital  ca- 
pacitjr.  It  has  been  shown  that  the  enlargement  of  the  heart  at  high 
altitudes  is  the  result  of  the  greater  demands  made  upon  that  organ 
during  physical  exertion.  If  the  chest  should  be  found  larger  among 
the  inhabitants  of  high  altitudes  it  likewise  may  be  explained  by 
the  increased  demand  made  upon  the  breathing  during  muscular 
effort.  The  immediate  effect  of  altitude  is  to  cause  a  slight  de- 
crease in  the  vital  capacity.  A  comparison  made  of  men,  at  a  low 
and  high  altitude,  indulging  in  outdoor  sports,  would  show  that  the 
vital  capacity  and  the  chest  measurements  are  similar.  Use  makes 
the  organ,  and  the  size  of  the  chest  depends  upon  the  demands  made 
in  breathing  by  physical  exertion  during  the  period  of  growth. 

THE  OXYGEN  PRESSURE  OF  THE  ARTERIAL  BLOOD  AT  HIGH  ALTITUDES. 

The  problem  which  concerns  us  here  is  to  determine  the  forces  by 
which  oxygen  is  transported  from  the  alveolar  air  of  the  lungs  into 
the  blood.  With  increasing  altitudes  the  air  is  reduced  and  oxygen 
tension  becomes  lower  and  lower.  At  a  height  of  about  15,000  feet 
the  barometric  is  little  over  half  that  of  atmospheric  pressure  and  the 
oxygen  tension,  therefore,  only  about  11  per  cent  of  an  atmosphere. 
As  has  been  pointed  out,  the  presence  of  man  at  any  considerable 
altitude  necessitates  adjustment  on  his  part  so  that  the  persistent  un- 
diminished  oxygen  requirement  of  the  body  can  be  satisfied  under 
the  enforced  changes  of  atmospheric  conditions.  Three  of  the  pos- 
sible means  of  providing  the  necessary  oxygen  have  already  been  dis- 
cussed. The  fourth  possibility  is  still  under  debate  among  physi- 
ologists. All  the  symptoms  of  altitude  sickness,  due  to  the  dimin- 
ished barometric  pressure,  depend  directly  or  indirectly  upon  the 
diminution  of  arterial  oxygen  pressure  and  the  consequent  imperfect 
aeration  of  the  arterial  blood  and  deficient  saturation  of  its  hemo- 
globin with  oxygen. 

The  passing  of  oxygen  from  the  alveolar  air  into  the  blood  of  the 
lung  capillaries  may  be  wholly  the  result  of  diffusion  of  oxygen,  in 
which  case  it  would  pass  from  a  place  of  high  to  one  of  low  pressure. 
If  oxygen  passes  from  the  alveoli  only  by  diffusion,  the  pressure  of 
oxygen  in  the  blood  will  always  be  less  than,  or  at  the  best  equal  to 
the  alveolar  oxygen  tension.  If  the  pressure  of  oxygen  in  the  blood 
is  under  certain  circumstances,  higher  than  that  of  the  aHeolar  air 
there  can  be  no  doubt  that  forces  other  than  diffusion  must  come  into 
play.  This  would  necessitate  an  active  secretion  by  the  epithelial  cells 
of  the  lungs.  At  sea  level,  during  rest,  the  arterial  oxygen  pressure  is 
practically  identical  with  the  alveolar  oxygen  pressure.  The  Anglo- 
American  Pike's  Peak  Expedition  in  1911  made  a  careful  study  of  the 
arterial  oxygen  pressure  and  found  in  every  case  that  the  arterial  oxy- 


30  MANUAL  OP  MEDICAL  EESEAECH   LABORATORY. 

gen  pressure  in  men  on  Pike's  Peak  was  much  above  tl;e  alveolar  oxy- 
gen pressure.  The  average  excess  of  oxygen  pressure  in  the  arterial 
blood  was  35.8  mm. ;  the  mean  normal  resting  alveolar  oxygen  pressure 
52.5  mm. ;  the  arterial  oxygen  pressure,  therefore,  88.3  mm.  The  alveo- 
lar oxygen  pressure  at  sea  level  is  about  100  mm.  and  that  of  the  blood 
about  the  same.  At  sea  level  the  arterial  blood  is  96  per  cent  satu- 
rated with  oxygen,  while  on  Pike's  Peak,  if  the  changes  of  acclimati- 
zation are  well  established,  it  is  95  per  cent  saturated.  One  subject 
was  examined  within  an  hour  after  reaching  the  summit  of  Pike's 
Peak  by  railway.  His  face  had  a  distinctly  bluish  color  and  he  suf- 
fered somewhat  severely  from  mountain  sickness  during  the  ensuing 
24  hours.  At  this  time — the  time  of  the  experiment — his  arterial 
oxygen  pressure  was  52.7  millimeters,  or  only  7  millimeters  above 
the  alveolar  oxygen  pressure.  Three  days  later,  when  he  had  become 
acclimated,  feeling  perfectly  well  and  with  normal  color,  the  arterial 
oxygen  pressure  was  81.4  millimeters,  or  40.7  millimeters  above  the 
alveolar  oxygen  pressure.  These  results  are  very  striking  and  point 
consistently  to  the  conclusion  that  in  acclimatization  to  high  altitudes 
the  lungs  acquire  the  power  of  raising  the  arterial  oxygen  pressure 
by  actively  secreting  oxygen. 

Certain  indirect  evidences  support  this  theory  of  oxygen  secretion. 
It  was  found  on  Pike's  Peak,  on  saturating  the  blood  with  alveolar 
air  in  a  saturator,  that  the  blood  was  noticeably  dark  in  color  as  com- 
pared with  the  blood  when  drawn.  It  is  well  known  that  men  can 
live  and  work  at  higher  altitudes  than  that  of  Pike's  Peak.  In  the 
explorations  of  the  Duke  of  the  Abruzzi  in  the  Himalayas  he  and  his 
companions  climbed  to  an  altitude  of  24,580  feet;  the  atmospheric 
oxygen  pressure  saturated  in  inspiration  would  be  55.4  millimeters 
and  the  alveolar  oxygen  pressure  only  21  millimeters.  Blood  satu- 
rated with  alveolar  air  at  this  pressure  would  be  less  than  half  satu- 
rated with  oxygen,  which  is  the  percentage  found  in  the  arterial 
blood  of  animals  at  the  point  of  death  from  asphyxia.  Nevertheless, 
at  this  altitude  the  members  of  the  expedition  felt  well  and  were  able 
to  do  the  climbing  necessary  in  attaining  the  altitude.  The  recent 
advances  in  knowledge  as  to  the  blood  gases  and  the  physiology  of 
respiration  make  it  difficult  to  explain  by  the  simple  diffusion  theory 
the  reactions  above  quoted.  Haldane  and  his  colaborators  have 
found  that  at  sea  level  muscular  work  may  furnish  a  powerful  stimu- 
lus to  secretory  absorption  of  oxygen  by  the  lung  epithelia  tissue. 
Therefore  one  advantage  in  indulging  in  heavy  muscular  work 
would  be  to  train  the  lungs  in  oxygen  secretion. 

THE  VALUE  OF  THE  FACTORS  OF  ACCLIMATIZATION. 

The  acclimatization  to  oxygen  want  in  mountaineers  or  persons 
living  at  high  altitudes  is  evidently  attributable  to  four  factors: 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  31 

The  increased  breathing,  the  increased  percentage  of  hemoglobin, 
the  increased  rate  of  blood  flow,  and  the  increased  oxygen  tension  in 
the  blood,  the  result  of  increased  activity  of  the  lung  epithelium. 

There  are  varying  degrees  of  susceptibility  to  want  of  oxygen 
among  any  group  of  men  exposed  to  low  barometric  pressure.  With 
a  rapidly  falling  oxygen  pressure  some  persons  simply  become  blue 
and  lose  consciousness  without  the  adaptive  mechanisms  of  the  body 
making  any  evident  response.  Men  who  are  fortunate  enough  to 
possess  brain  centers  sensitive  to  oxygen  want  will  respond  quickly 
to  the  stimulus  of  a  lack  of  oxygen  and  either  escape  or  have  only  a 
mild  attack  of  mountain  sickness.  On  the  other  hand,  those  with  an  in- 
sensitive nervous  mechanism  will  fail  to  respond,  or  be  so  slow  in  doing 
so  that  a  period  of  altitude  sickness  must  be  expected.  This  sickness 
will  begin  to  wane  when  the  adaptive  changes  begin  to  be  manifest. 
There  are  marked  individual  differences  which  are  no  doubt  asso- 
ciated in  some  way  with  the  freedom  of  the  blood  supply  to  the  brain. 
Ordinarily  on  ascending  a  mountain  the  respiratory  adjustment 
occurs  first,  beginning  almost  at  once;  it  requires,  however,  several 
weeks  to  become  complete.  After  some  delay  the  blood  changes,  the 
increase  in  the  rate  of  blood  flow,  and  the  so-called  oxygen  secretion 
manifest  themselves.  The  order  of  their  onset  and  the  rapidity  of 
development  will  depend  on  the  physical  condition  of  the  individual 
and  the  sensitiveness  of  the  brain  centers  to  low  oxygen. 

There  is  at  the  start  a  rapid  increase  in  each  of  the  factors  in- 
volved, followed  by  a  more  gradual  continuation  of  the  effect  extend- 
ing over  some  weeks.  The  increase  in  the  rate  of  blood  flow  and  the 
oxygen  secretion  by  the  lungs  are  developments  of  the  first  two  or 
three  days  spent  at  the  high  altitude.  The  blood  changes,  while 
rapid  during  the  first  few  days,  require  more  than  five  weeks  to  reach 
their  maximum  value.  The  changes  in  the  breathing,  the  blood,  and 
in  oxygen  secretion  are  of  a  permanent  character  and  will  not  di- 
minish with  a  prolonged  residence  at  the  high  altitude.  The  changes 
in  the  rate  of  blood  flow  are  of  a  less  permanent  character ;  with  the 
acclimatization  the  pulse  rate  returns  somewhat  toward  the  sea-level 
values.  Undoubtedly  the  heart  is  under  a  greater  strain  during  the 
early  days  spent  at  a  high  altitude  than  later,  when  the  adaptive 
changes  have  been  completed.  Physical  fitness  usually  assures  an 
early  and  rapid  response  to  the  stimulating  effects  of  low  oxygen  at 
the  high  altitude.  Fatigue  and  other  debilitating  causes  delay  the 
response  and  make  the  individual  more  liable  to  an  attack  of  altitude 
sickness. 

The  longer  the  period  of  sojourn  at  a  high  altitude  the  more  perma- 
nently fixed  become  the  altitude  adaptive  changes.  This  fact  has 
been  proven  by  studies  on  the  after  effects  of  high  altitudes  in  those 
who  return  toward  sea  level.  If  the  sojourn  at  the  high  altitude  were 


32  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

of  a  short  duration,  only  a  few  days,  on  returning  the  blood  is  re- 
stored almost  immediately  to  its  normal  composition.  The  breathing 
likewise  at  once  takes  on  the  normal  depth  and  rate.  After  a  so- 
journ of  five  weeks  on  Pike's  Peak  the  after  effects  on  descending 
were  shown  to  be  present  for  a  period  of  at  least  two  weeks.  At  the 
end  of  a  six  months  stay  at  the  same  altitude  the  percentage  of  hemo- 
globin, number  of  red  corpuscles,  total  volume  of  blood,  and  total 
oxygen  capacity  did  not  alter  at  once  and  were  at  least  10  weeks  in 
being  restored  to  the  low-altitude  values.  The  breathing  for  24  hours 
was  as  great  as  when  at  14,110  feet  and  then  slowly,  throughout  a 
period  of  10  weeks,  decreased  to  the  normal  for  the  lower  altitude. 
The  first  days  after  descending,  the  pulse  rate  was  about  10  beats  be- 
low the  normal  for  the  low  altitude,  but  later  accelerated  to  the  nor- 
mal for  the  particular  altitude. 

The  study  of  the  after  effects  indicates  that  the  aviator  remains  at 
the  high  altitudes  too  short  a  period  of  time  to  secure  permanent 
adaptive  reactions  which  increase  toleration  of  high  altitudes.  Re- 
peated experiments  in  pneumatic  chambers  and  with  carbon  monoxide 
occasionally  have  increased  in  some  men  the  ability  to  tolerate  low 
oxygen.  The  experience  in  aviation  indicates  that  the  changes  in 
altitude  during  flying  are  made  so  rapidly  that  the  compensating 
mechanisms  for  low  oxygen  are  overworked  to  a  greater  or  less  degree, 
and  as  a  consequence  instead  of  securing  acclimatization  to  low 
oxygen  a  weakening  of  the  adjusting  mechanisms  occurs,  which  ren- 
ders the  flier  more  liable  to  an  attack  of  altitude  sickness. 

PHYSICAL   FITNESS    AND   THE   ABILITY   TO   WITHSTAND    HIGH    ALTITUDES. 

The  ability  to  endure  comfortably  and  well  high  altitudes  is  de- 
pendent upon  the  ease  and  the  quickness  with  which  the  adaptive 
responses  in  the  breathing,  the  blood,  and  the  circulation  take  place. 
An  explanation  of  the  difference  in  reaction  observed  among  the  mem- 
bers of  a  group  of  men  when  at  a  high  altitude  is  to  be  found  in  the 
degree  of  individual  physical  fitness.  In  persons  damaged  by  dis- 
ease, overwork,  unhygienic  living,  or  weakened  by  inactivity  and  by 
loss  of  sleep,  the  power  of  adjustment  is  as  a  rule  below  par.  The 
normal  equilibrium  of  the  body  is  so  nicely  adjusted  that  under  usual 
conditions  the  physiological  balance  is  largely  maintained  by  adjust- 
ments that  are  made  with  little  or  no  expenditure  of  energy.  There 
is  a  certain  range  of  greater  or  less  breadth  through  which  the  exter- 
nal factors  of  the  environment  may  be  varied  and  yet  be  met  by  an 
automatic  adjustment  of  the  physiological  processes  in  the  body 
which  will  preserve  the  vital  balance  of  the  mechanism.  But  beyond 
a  certain  point,  specific  for  each  organism,  changes  in  the  external 
conditions  will  necessitate  more  radical  alterations  which  will  tax 
the  compensating  mechanisms  to  the  utmost  capacity  in  order  to  pre- 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 


33 


vent  disaster.  Theoretically  the  organism  which  has  been  called  upon 
repeatedly  to  make  a  certain  kind  of  adjustment  will  be  the  one  most 
capable  of  responding  when  an  extraordinary  demand  is  made.  The 
unusual  demand  made  upon  the  organism  at  a  high  altitude  is  that 
of  supplying  the  requisite  amount  of  oxygen  to  the  tissues  from  an 
atmosphere  that  provides  oxygen  at  a  greatly  reduced  pressure.  An 
organism  that  has  always  been  able  to  supply  its  oxygen  needs  with- 
out profound  or  costly  changes  because  the  demands  for  oxygen  have 
never  been  excessive  or  the  oxygen  supply  has  never  been  reduced 
will  most  likely  not  readily  respond  when  it  meets  a  shortage  of 
oxygen.  In_the  everyday  experiences  of  life  there  arises  a  marked  in- 
crease in  the  demand  for  oxygen  during  physical  exertion.  Excessive 
exertion  may,  of  course,  call  for  so  much  oxygen  that  the  adjustments 
of  the  15ody  may  fail  to  provide  sufficient  quantity  for  complete1 
combustion  in  the  muscles.  That  this  is  often  the  case  is  proven  by 
the  great  production  of  lactic  acid  during  physical  work.  Since 
physical  exertion  does  increase  the  demand  for  oxygen  it  is  to  be 
expected  that  the  organism  which  has  been  called  upon  to  do  physical 
work  frequently  will  have  acquired  marked  powers  for  compensating 
for  oxygen  want. 

Comparisons  made  of  animals  leading  a  muscularly  inactive  life 
with  those  of  a  closely  related  species  whose  mode  of  living  calls  for 
much,  running  and  great  physical  endurance  show  certain  well- 
defined  "differences  attributable  to  muscular  action  and  the  call  for 
oxygen.  It  has  been  found  that  the  active  animal  has  a  heart  which 
relatively  is  three  or  four  times  heavier  than  that  of  the  inactive 
animal.  Also  the  rate  of  the  heart  beat  is  much  slower — only  about 
a  third — the  rate  of  respiration  less,  the  depth  of  breathing  greater, 
and  the  percentage  of  hemoglobin  greater  in  the  active  than  in  the 
inactive  animal.  Furthermore,  the  flesh  of  the  active  animal  is 
darker  in  color,  due  to  the  presence  of  a  larger  amount  of  myohe- 
matin — the  substance  with  marked  affinity  for  oxygen.  These  differ- ' 
ences  are  undoubtedly  adaptive  and  fit  the  organism  to  supply  the 
tissues  with  the  extra  amount  of  oxygen  required  during  exertion. 

The  adaptive  characters  found  in  physically  active  animals  are  very 
like  those  that  appear  in  the  body  of  man  when  he  follows  a  regular 
and  consistent  course  of  physical  training,  and  they  likewise  are 
characteristics  which  will  permit  the  individual  to  tolerate  well  high 
altitudes.  Comparisons  made  of  athletic  and  nonathletic  individuals 
show  that  the  athletic,  or  better,  the  physically  fit  persons  possess  cer- 
tain physiological  conditions  of  advantage  at  high  altitudes. 

In  the  physically  fit  the  daily  indulgence  in  physical  exercise  will 
be  found  to  have  increased  the  percentage  and  the  total  amount  of 

89119—18 3 


34  MANUAL  OF   MEDICAL  BESEARCH   LABOKATOBY. 

hemoglobin  in  the  blood.  With  this  advantage,  if  he  goes  to  a  high 
altitude,  he  quickly  responds  to  the  stimulating  influence  of  oxygen 
shortage  by  throwing  into  the  circulation  the  reserve  supply  of 
corpuscles  and  by  further  concentration  of  the  blood.  Consequently 
the"  tissues  are  supplied  with  blood  which  per  unit  of  volume  is  richer 
in  oxygen,  .than  it  would  be  if  the  hemoglobin  were  less  concentrated. 
In  the  untrained  man  there  is  less  hemoglobin,  and  the  changes  in- 
duced by  altitude  occur  so  slowly  that  he  will  most  likely  suffer  with 
altitude  sickness  because  of  oxygen  want. 

In  the  physically  well  trained  the  breathing  is  slow  and  deep,  while 
in  the  untrained  it  is  shallow  and  rapid.  Deep  breathing,  which  can 
be  cultivated  by  exercise,  but  not  satisfactorily  by  voluntary  atten- 
tion, ventilates  the  lungs  more  effectively  than  shallow  breathing; 
therefore  at  a  high  altitude  there  is  advantage  in  being  a  deep 
breather.  It  also  can  be  shown  that  the  breathing  of  the  physically 
fit  man  responds  quickly  and  well  to  the  high  altitude  demand  for 
more  oxygen,  while  in  the  untrained  it  will  be  slower  in  doing  so. 

At  sea  level  moderate  muscular  work  does  not  create  a  great  de- 
mand for  oxygen,  but  strenuous  and  prolonged  exertion  may  tax  the 
oxygen-providing  mechanisms  to  their  utmost  capacity.  In  order 
to  meet  this  increased  demand  for  oxygen  the  lungs  may  respond  by 
secreting  oxygen  into  the  blood.  Repeated  demands  for  oxygen  secre- 
tion would,  so  to  speak,  train  the  lung  epithelium  for  the  unusual 
work.  It  is  suggested  that  such  a  reaction  by  the  lungs  would  be 
valuable  when  one  ascends  to  high  altitudes,  in  that  the  lungs  would 
then  immediately  begin  to  secrete  oxygen.  Oxygen  secretion  is  in  the 
nonathletic  type  of  individual  acquired  only  after  several  days  of  res- 
idence at  a  high  altitude,  but  in  the  vigorous  well-trained  man  it  prob- 
ably begins  almost  immediately. 

As  a  result  of  physical  training  the  heart  reduces  its  rate  of  beating 
and  is  less  sensitive  to  changes  in  posture  and  to  moderate  exertion. 
In  the  physically  fit  the  heart  rate  does  not  increase  much  on  standing, 
but  in  the  wearied  or  physically  stale  subject  it  increases  as  much  as 
44  beats  per  minute.  The  vasomotor  control  of  the  splanchnic  area 
in  man  experiences  a  change  of  adjustment  when  the  body  is  moved 
from  the  horizontal  to  the  upright  standing  position.  In  a  robust 
subject  the  splanchnic  vasotone  increases  and  the  blood  pressure  is 
raised  about  10  millimeters  of  mercury.  In  an  individual  weakened 
by  dissipation,  overwork,  lack  of  sleep,  etc.,  the  blood  pressure  tends 
not  to  rise,  but  to  fall.  'Weakness  is  sometimes  shown  by  a  decrease 
in  blood  pressure  and  at  other  times  by  an  excessive  increase  in  the 
heart  rate. 

At  a  high  altitude,  especially  during  the  first  days  of  residence, 
any  physical  exertion  makes  a  greater  demand  on  the  heart  than  the 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


35 


same  amount  of  work  at  sea  level.  In  the  nonathletic  individual  the 
heart  reacts  excessively  us  a  result  of  \vork.  while  in  men  in  excellent 
physical  condition  the  reaction  at  a  high  altitude  is  less  and  the  strain 
on  the  heart  will,  therefore,  be  much  less.  A_trained  hearty  like  a 
trained  muscle,  works  more  smoothly  and  easily  ilnm  the  untrained, 
and  therefore  endures  fatiguing  work  better  than  the  untrained  heart. 

-Medical  experience  with  the  "  stale  pilot "  and  the  "  stale  athlete  " 
has  shown  that  as  a_jman  becomes  stale  his  pysiological  condition  re- 
veils  to  that  of  (he  nonathletic  type  of  individual.  Staleness  is  rec- 
ognized by  an  increased  frequency  of  pulse,  which  is  also  poor  in 
volume  and  low  in  tension.  There  will  be  distress  on  slight  exertion, 
accompanied  by  a  rapid  rise  in  the  pulse  rate,  which  returns  only 
after  a  long  interval  to  its  former  rate.  The  breathing  also  fre- 
quently becomes  shallow  and  rapid,  and  the  extremities  become  poor 
in  color  and  cold  because  of  poor  circulation. 

Most  of  the  symptoms  reported  as  common  among  aviators  while 
flying  are  those  that  are  characteristic  of  mountaiiLaickness.  It  has 
been  shown  that  mountain  sickness  is  not  so  common  among  robust 
as  among  individuals  of  sedentary  habits  of  living.  We  may  venture 
to  conclude,  therefore,  that  the  man  who  is  in  the  "pink  of  condi- 
tion" as  a  result  of  consistent  and  common-sense  physical  training 
will  be  more  resistent  to  the  action  of  altitude  than  the  untrained  or 
the  physically  stale  man. 

Medical  experience  with  "stale"  aviators  shows  a  type  known  as 
the  nervous  in  which  there  is  poor  muscular  control  over  balance 
movements,  fine  tremors  of  the  hands  and  eyelids,  greatly  increased 
reflexes,  loss  of  sleep,  nightmares,  and  apprehensive  starts  with 
slight  noise.  The  influence  of  high  altitudes  on  the  nervous  system 
has  not  been  carefully  studied,  but  there  are  those  who  believe  that 
in  persons  with  poor  compensation  and  an  unstable  nervous  system 
there  is  increased  irritability  or  hyperexcitability  which  may  mani- 
fest itself  in  motor,  sensory,  or  psychic  spheres,  or  in  a  combination 
of  them.  Associated  with  the  increased  excitability  there  is  in- 
creased rapidity  of  fatigue  which  finds  expression  in  muscular  weak- 
ness and  diminished  physical  endurance,  as  well  as  failure  in  adapt- 
abilitjr  and  power  of  concentration  mentally.  Such  persons  complain 
of  a  mental  unrest,  approaching  anxiety,  and  find  difficulty  in  carry- 
ing on  the  usual  mental  requirements  of  their  occupations.  Such  a 
condition  may  be  the  forerunner  of  a  simple  neurasthenia  or  a  more 
profound  neurosis. 

The  nervous  system  is  exceedingly  sensitive  to  'oxygen  want.  It 
is  significant,  therefore,  that  in  the  nervous  system  arrangements  are 
provided  for  a  free  supply  of  oxygen.  The  lack  of  oxygen  at  high 
altitudes  is  felt  by  all  body  tissues,  but  especially  by  the  nervous 


36 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


tissues.  It  seems  to  be  established  that  there  is  an  irritability  of  the 
nervous  system  that  may  be  attributed  to  diminished  oxygen  supply 
by  reason  of  a  failure  on  the  part  of  certain  individuals  to  compen- 
sate adequately  to  lack  of  oxygen  when  at  the  high  altitude. 

Relation  of  altitude,  pressure,  and  oxygen. 


mm.  HG. 

Elevation. 

02. 

mm.  HG. 

Elevation. 

Of 

760                    

Feet. 
0 

Per  cent. 

20.  90 

412  

Feet. 
16,000 

Per  cent. 
11.39 

732                    

1,000 

20.15 

397  

17,000 

10.97 

704 

2  000 

19  38 

382           

18,000 

10.  56 

677 

3  000 

18.  64 

368           

19,000 

10.16 

651 

4  000 

17.93 

354           

20,000 

9.78 

626                          

5,000 

17.25 

341           

21,000 

9.41 

602 

6  000 

16  CO 

328               

22  000 

9.05 

579           

7,000 

15.97 

315  

23,000 

8.70 

557           

8,000 

15.37 

303  

24,000 

8.35 

536                             

9  000 

14.80 

290           

25,  000 

8.01 

516               

10  000 

14.  25 

278         

2t'i,  000 

7.68 

497               

11,000 

13.73 

2-'>6  

27,000 

7.35 

478         

12,000 

13.23 

251  

28,000 

7.03 

461                             .   . 

13  000 

12  75 

242         

29  000 

6.71 

444                          .   . 

14  000 

12.28 

230         

30  000 

6.40 

428   

15,000 

11.83 

In  order  that  the  reasoning  which  led  to  the  development  of  the 
rebreathing  apparatus  and  the  study  of  man  under  rebreathing  may 
be  understood,  it  will  be  necessary  to  insert  here  a  brief  statement 
concerning  our  knowledge  of  the  effects  of  high  altitudes.  It  has 
been  known  for  a  long  time  that  man  living  at  extremely  high  alti- 
tudes may  develop  what  is  popularly  known  as  "joipuntainsickness," 
during  which  he  exhibits  certain  definite  symptoms.  Alter  a  shorter 
or  longer  period  of  sojourn  at  the  high  altitude,  these  symptoms 
pass  away  and  acclimatization  takes  place.  During  the  last  40  years, 
but  more  particularly  the  last  18  years,  physiologists  have  been  care- 
fully investigating  "  mountain  sickness  "  and  the  adaptive  changes 
that  occur  in  the  body  of  man  and  animals  living  at  great  altitudes. 
There  has  come  from  this  study  almost  complete  agreement  of  the 
investigators.  There  is,  in  fact,  no  room  now  for  doubt  that  the  essen- 
tial cause  of  all  the  symptoms  of  altitude  sickness  and  the  adaptive 
changes  within  the  body  is  the  lack  ..oJLoxygen,  which  is  the  result 
of  the  rarefaction  of  the  air  that  occurs  as  altitude  increases.  The 
fact  that  there  is  oxygen  want  at  high  altitudes  suggested  the  fact 
that  any  mechanism  that  would  permit  the  breathing  of  a  reduced 
amount  of  oxygen  could  be  used  to  test  the  ability  of  men  to  with- 
stand the  effects  of  low  oxygen.  The  rebreathing  apparatus  was 
designed  not  only  to  expose  man  to  low  oxygen  but  to  a  constantly 
decreasing  amount  of  oxygen.  A  description  of  the  apparatus  and 
the  method  of  use  will  be  found  elsewhere  in  this  report. 

In  order  that  oxygen  percentages  may  be  translated  into  altitudes, 
the  relation  of  altitude  and  oxygen,  as  well  as  altitude  and  pressure, 


MANUAL  OF  MEDICAL  EESEAECH   LABORATORY. 


37 


are  shown  in  chart  1.  On  referring  to  the  12  per  cent  oxygen  line, 
it  will  be  observed  that  wh^nthe_subject  of  experimentation  is  breath- 
ing 12  per  cent  oxygen,  he  is  physiologically  at  an  altitude  of  14,400 
feet,  and  when  breathing  10  per  cent  oxygen  the  equivalent  altitude 
is  19,400  feet. 

One  purpose  in  the  method  of  examining  aviators  by  rebreathing 
is  to  reproduce  the  gradually  decreasing  oxygen  tension  that  they 
will  experience  as  they  ascend  in  the  air.  A  sudden  disturbance  of 
bodily  functions  usually  is  manifested  by  symptoms  of  illness.  The 
disturbance  brought  about  by  changes  of  altitude  and  by  low  oxygen 
cause  the  so-called  "altitude  sickness."  Individuals  differ  greatly 
in  the  power  of  resistance.  Hence,  we  find  that  altitude  sickness 


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CHART  1. 

attacks  some  at  a  lower,  others  at  a  higher  altitude,  but  it  is  also 
certain  that  no  one  who  proceeds  beyond  the  elevation — that  is,  the 
critical  line  for  him — escapes  the  malady.  An  elevation  of  10.000 
feet,  or  even  less,  may  provoke  it  in  some;  others  may  escape  up  to 
14,000  feet  or  even  17,000  feet;  while  only  a  few  possessed  of  un- 
usual resisting  power  can,  without  pronounced  symptoms,  venture 
upward  to  18,000  feet.  The  flier  himself  may  not  be  conscious  of 
the  symptoms  when  they  first  appear.  The  degree  of  illness  will  be 
determined  by  the  length  of  time  the  subject  is  exposed  to  oxygen 
want.  In  the  rebreathing  experiments  WTC  produce  artificially  a 
mild  attack  of  altitude  sickness.  The  percentage  of  oxygen  at  which 
the  symptoms  appear  will  indicate  the  altitude  at  which  similar 


38  MANUAL   OF    MEDICAL   RESEARCH    LABORATORY. 

symptoms  may  be  expected  to  occur,  provided  the  length  of  time 
given  to  the  rebreathing  experiment  has  not  been  .too  short. 
Throughout  rebreathing  experiments  attention  has  been  directed  to 
a  stud}7  of  the  pulse  rate,  the  arterial  blood  pressure  changes,  the 
character  and  the  volume  of  the  breathing,  and  to  the  color  changes 
in  the  skin  and  mucous  membranes.  It  is  well  to  recall  here  that  in 
an  attack  of  "  mountain  sickness  "  the  pulse  rate  is  always  accelerated 
and  the  systolic  and  diastolic  pressures  are  higher  than  in  normal 
life.  The  patient  may  feel  slightly  giddy  and  there  may  be  buzzing 
in  the  ears,  dimmed  sight,  and  fainting  attacks.  The  face  may  be 
cyanosed  and  the  eyes  look  dull  and  heavy.  In  some  degree  all  of 
these  conditions  may  occur  as  the  subject  undergoes  the  exposure  to 
low  oxygen  tension  during  a  rebreathing  experiment.  Many  of  the 
reactions  here  called  "  symptoms,"  which  occur  under  low  oxygen 
tension  at  high  altitudes  and  during  a  rebreathing  experiment,  are 
simply  compensatory  changes  by  which  nature  endeavors  to  keep  the 
tissues  abundantly  supplied  with  oxygen. 

II.— THE  PHYSIOLOGY   OF  REBREATHING  AND   AVIATION. 

The  physiological  observations  made  on  men  and  animals  living 
at  high  altitudes  or  under  reduced  atmospheric  pressures  show  clearly 
that  a  very  marked  process  of  adaptations  occurs  which  renders  the 
mechanism  capable  of  meeting  the  call  of  the  tissues  for  oxygen.  The 
aviator  must  also  be  able  to  adapt  himself  physiologically  to  altitude 
changes.  The  aviator  does  not  remain  at  high  altitudes  long  enough 
to  benefit  from  slow  adaptive  physiological  changes,  therefore  his 
body  must  be  capable  of  making  rapid  compensatory  changes  which 
will  provide  the  oxygen  needed  by  the  tissues.  He  must  be  able  to 
bear  abrupt  and  great  changes  in  atmospheric  pressure.  Without 
the  occurrence  of  some  one  or  more  definite  adaptive  physiological 
responses  to  provide  for  his  oxygen  needs  as  he  ascends,  his  life  and 
aeroplane  become  more  and  more  jeopardized  as  he  continues  to 
ascend. 

That  the  body  can  and  does  respond  to  the  demands  for  oxygen 
during  rapid  ascents  has  been  proven  by  laboratory  experiments  and 
the  experience  of  aviators  and  balloonists.  The  physiological  re- 
sponses that  are  definite,  like  those  experienced  by  the  mountaineer, 
are  an  increased  ventilation  of  the  lungs  and  a  more  rapid  blood  flow. 
In  a  few  men  a  concentration  of  the  blood  may  also  occur. 

It  has  been  clearly  established  that  the  essential  cause  of  the 
adaptive  changes  within  the  body  when  at  high  altitudes  is  the  lack 
of  oxygen,  which  is  due  to  the  rarefaction  of  the  air  that  occurs  as 
altitude  increases.  The  fact  that  there  is  this  oxygen  want,  suggested 
that  any  mechanism  that  would  permit  the  breathing  of  a  reduced 
amount  of  oxygen  could  be  used  to  test  the  ability  of  men  to  with- 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  39 

stand  high  altitudes.  The  rebreathing  apparatus  has  been  per- 
fected for  4such  tests.  During  the  tests  the  subject  breathes  the 
air  in  the  tank.  He  sits  with  a  clip  placed  on  the  nose  and  with 
a  comfortably  adjusted  mouthpiece  in  the  mouth,  which  is  suitably 
connected  by  means  of  inch  tubing  with  light  automatic  valves.  He 
inhales  the  air  through  the  respiratory  valve  direct  from  the  tank  and 
exhales  through  the  expiratory  valve  into  a  cartridge  containing  an 
absorbent  for  carbon  dioxide.  The  exhaled  air  is  thus  freed  from 
carbon  dioxide  as  it  is  returned  to  the  tank.  A  spirometer  compen- 
sates for  changes  in  volume  and  writes  a  record  of  the  respiration 
upon  the  revolving  drum  of  a  kymograph.  By  this  arrangement  the 
subject  continues  to  rebreathe  the  air  in  the  tank  from  which  he 
gradually  absorbs  oxygen.  As  the  percentage  of  oxygen  decreases, 
the  subject,  in  effect  physiologically,  is  slowly  ascending  to  higher 
altitudes.  The  volume  of  air  rebreathing  is  sufficient  to  require  be- 
tween 25  and  30  minutes  to  lower  the  amount  of  oxygen  to  8  or  7  per 
cent,  which  is  equivalent  to  altitudes  of  25,000  to  28,000  feet. 

A  COMPARISON  OF  THE  REBREATHING  TEST  AND  THE  DILUTION  TEST. 

Comparisons  to  date  of  the  rebreathing  and  dilution  tests  upon  the 
same  individuals  show  a  marked  similarity  in  the  reactions  which 
occur  and  demonstrate  conclusively  that  the  adaptive  changes  occur- 
ring in  both  cases  are  due  to  low  oxygen. 

The  dilution  apparatus 1  used  in  our  laboratory  is  an  arrangement 
whereby  it  is  possible  to  let  pure  atmospheric  air  or  a  mixture  of 
atmospheric  air  and  nitrogen  pass  into  a  breathing  chamber  and  ac- 
cordingly, at  will,  change  the  relative  proportions  between  atmos- 
pheric air  and  nitrogen.  This  permits  of  changing  the  partial  pres- 
sure of  oxygen  at  any  desired  rate,  thus  producing  the  same  effect  as 
if  the  partial  pressure  of  oxygen  were  reduced  by  mounting  in  the 
air. 

The  rebreathing  machine  is  an  apparatus  whereby  the  subject  re- 
breathes  a  specified  amount  of  air  from  a  tank,  thereby  causing  a 
gradual  and  progressive  decrease  of  the  oxygen.  The  CO2  of  the 
expired  air  is  removed  by  an  absorbent  and  therefore  is  not  a  factor 
in  the  test. 

Both  tests  are  essentially  low  oxygen  tests,  as  the  nitrogen  and  CO2 
play  no  part  in  producing  any  of  the  adaptive  changes. 

The  similarity  and  parallelism  of  the  reactions  in  both  tests  upon 
the  same  individuals  are  marked. 

A  comparison  of  many  charts  showed  the  average  point  of  accel- 
eration of  the  pulse  to  be  the  same  in  both  the  Dilution  Test  and  the 
Rebreathing  Test.  Also  the  limits  of  compensation  for  the  systolic 
and  diastolic  were  the  same  in  both.  A  fall  in  the  systolic  at  a  cer- 

1  See  Reports  of  the  Air  Medical  Investigation  Committee,  No.  2,  England. 


40  MANUAL   OP    MEDICAL  RESEARCH    LABORATORY. 

tain  percentage  of  oxygen  in  the  Rebreathing  Test  was  almost  invari- 
ably accompanied  by  a  fall  in  the  systolic  at  the  same  percentage  of 
oxygen  in  the  Dilution  Test.  The  same  was  true  of  the  pulse  rate 
and  diastolic  pressure. 

Throughout  rebreathing  experiments  physiological,  psychological, 
and  other  observations  are  made  on  the  subject  of  the  test.  By  the 
physiologist,  the  rate  and  per  minute  volume  of  respiration,  pulse 
frequency,  systolic  and  diastolic  arterial  pressures  are  studied  for 
each  candidate  tested  and  have  been  found  to  give  valuable  evidence 
as  to  when  he  first  responds  to  the  reduction  in  oxygen  and  as  to  the 
efficacy  of  his  compensatory  reaction.  Some  men  are  sensitive  to 
oxygen  want  and  compensate  in  their  breathing  and  circulation  of 
the  blood  so  that  they  endure  as  low  as  6  per  cent  of  oxygen.  Others 
fail  to  compensate  in  one  or  both  of  these  mechanisms  or  compensate 
inadequately  and,  therefore,  can  not  endure  so  low  an  oxygen  per 
cent.  All  gradations  between  failure  to  compensate  and  adequate 
compensation  down  to  6  per  cent  of  oxygen  have  been  found  among 
the  men  examined  under  the  low  oxygen  of  the  rebreathing  tests. 
From  the  data  obtained  during  the  rebreathing  test  it  becomes  pos- 
sible to  determine  approximately  the  maximum  altitude  to  which 
the  aviator  may  safely  ascend. 

THE  BREATHING  WHEN  UNDER  THE  ACTION  OF  PROGRESSIVE  DECREASE  IN 

THE  OXYGEN  SUPPLY. 

The  character  of  the  breathing  undoubtedly  has  an  important 
bearing  on  the  ability  of  men  to  endure  at  high  altitudes.  The  shal- 
low breather  is  at  a  greater  disadvantage  than  the  man  who  breathes 
deeply  when  under  the  influence  of  low  oxygen.  In  breathing  a 
part  of  the  fresh  air  remains  in  the  nose,  pharynx,  larynx,  trachea, 
and  bronchial  tubes  and  is  emptied  out  again  at  the  beginning  of  the 
next  expiration  in  an  almost  unchanged  condition,  without  having 
actually  mingled  with  the  air  in  the  alveoli  of  the  lungs.  In  shallow7 
breathing,  therefore,  only  a  comparatively  small  amount  of  the  fresh 
air  gets  past  this  so-called  dead  space  to  mingle  with  the  air  in  con- 
tact with  the  blood  vessels  of  the  lungs.  The  deeper  the  breathing 
the  greater  will  be  the  amount  of  fresh  air  that  reaches  the  aveoli 
of  the  lungs  and  hence  the  greater  will  be  the  supply  of  oxygen  for 
the  body  tissues. 

The  men  examined  have  shown  rates  of  breathing  when  sitting 
that  ranged  between  14  and  25  breaths  per  minute.  Between  40  and 
50  per  cent  breathed  at  the  rate  of  18  and  19  breaths  per  minute. 
The  per  minute  volume  of  breathing  ranged  between  7  and  12.5 
liters,  with  the  majority  between  8.5  and  9  liters.  The  average  tidal 
volume  of  air  breathed  was  500  cubic  centimeters  for  the  group, 
while  the  extremes  were  360  and  630  cubic  centimeters,  respectively. 


DREYER  LOW  OXYGEN  APPARATUS. 


40 


O  •;  •...,~.,..»....M»,«    Pulse    • •  -* »   Rest),  in  decil.  Dei-  nun 


H.F.D.K.,  Age  25-10/12 
Almost  a  record  run.   "Class  AA." 


Tl.MK  IX  MIXTTKS 


41 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  41 

The  smaller  volumes  of  tidal  air  were  found  among  subjects  who 
breathed  most  frequently.  Thus  one  man  who  breathed  24  times 
per  minute  had  a  tidal  air  volume  of  375  cilbic  centimeters,  while 
another  whose  rate  was  14  per  minute  had  a  tidal  air  volume  of  620 
cubic  centimeters.  A  slow,  deep  breathing  will,  as  a  rule,  introduce 
more  fresh  air  into  the  alveoli  of  the  lungs  than  the  shallowT,  rapid 
type  of  breathing. 

As  the  percentage  of  oxygen  gradually  decreases  during  a  re- 
breathing  test  there  occurs  a  marked  respiratory  response  to  the 
lessening  oxygen  tension  which  increases  the  amount  of  air  breathed 
per  minute.  This  increase  in  the  lung  ventilation  in  a  few  men 
begins  with  the  first  decrease  in  the  oxygen  percentage  of  the  air 
breathed  and  is  a  gradual  proportional  increase  in  inverse  ratio,  with 
the  reduction  in  oxygen.  Over  50  per  cent  of  the  men  examined  gave 
the  first  respiratory  response  between  16  and  14  per  cent  of  oxygen. 
Twenty-five  per  cent  responded  first  at  a  lower  oxygen  tension,  while 
a  small  number  of  men  gave  no  respiratory  response  to  the  decrease 
in  available  oxygen.  The  increase  in  lung  ventilation  is  for  the 
higher  percentage  of  oxygen  only  slight,  but  usually  becomes  more 
pronounced  when  the  available  oxygen  has  been  decreased  to  between 
12.5  and  9  per  cent.  (See  charts  1-6.) 

The  rate  of  breathing  for  many  men  remain  unchanged  throughout 
the  rebreathing  test.  The  majority,  however,  show  an  increase  of 
from  two  to  four  breaths  per  minute  at  between  8  and  6  per  cent 
of  oxygen.  A  few  of  the  men  examined,  shown  by  other  tests  to  be 
somewhat  physically  stale,  increased  the  frequency  of  breathing 
enormously.  Thus  one  subject,  with  a  frequency  of  22  when  sitting 
quietly  breathing  atmospheric  air,  breathed  43  times  per  minute 
at  8.5  per  cent  of  oxygen. 

The  amount  per  minute  volume  increase  in  the  breathing  during 
a  rebreathing  test  differs  with  individuals.  The  majority  of  men 
examined  show  at  per  centages  of  oxygen  between  8  and  0  per  cent 
an  increase  of  5.5  liters  over  the  volume  breathed  at  the  beginning 
of  the  experiment.  This  increase  gives  for  the  average  man  a  total 
volume  of  breathing  per  minute  of  approximately  14  liters  at  oxygen 
tensions  corresponding  to  an  altitude  of  25,000  feet.  The  total  per 
minute  volume  of  air  breathed  has,  in  exceptional  cases,  been  as 
great  as  26  and  37  liters  of  air  at  oxygen  tensions  corresponding  to 
from  25,000  to  28,000  feet. 

It  is  the  depth  of  breathing  which  ordinarily  is  increased  by  low 
oxygen.  The  vast  majority  of  subjects  show  an  increase  in  depth 
of  breathing  of  from  20  to  128  per  cent  when  under  8.5  to  6  per  cent 
oxygen.  The  volume  of  each  breath  in  these  men  if  found  to  range 
between  600  and  1,260  cubic  centimeters,  while  for  the  same  subjects 
when  sitting  quietly  breathing  atmospheric  air  the  tidal  volume  is 
found  to  range  between  360  and  630  cubic  centimeters. 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 

A  good  respiratory  reaction  to  the  gradual  decrease  in  the  oxygen 
of  a  rebreathing  test  will  be  manifest  in  a  slight  increase  in  the 
depth  of  breathing  which  begins  at  16  or  15  per  cent  oxygen  and 
continues  to  progressively  increase  slightly  and  gradually  until  12.5 
to  9  per  cent  of  oxygen.  From  these  percentages  down  to  8.5  and  6 
per  cent  of  oxygen  the  total  per  minute'  volume  of  breathing  increases 
much  more  rapidly  and  the  frequency  of  breathing  may  also  then 
increase  to  from  two  to  five  breaths  per  minute.  A  total  per  minute 
increase  of  at  least  5.5  liters  should  occur  at  the  lower  percentages 
of  oxygen.  The  increase  in  the  depth  of  breathing  which  occurs 
under  low  oxygen  more  effectively  ventilates  the  alveoli  of  the  lungs 
and,  therefore,  raises  the  alveolar  oxygen  tension  above  that  which 
would  be  present  if  the  breathing  remained  unchanged.  Such  an 
increase  in  alveolar  oxygen  permits  the  blood  to  be  more  thoroughly 
saturated  with  oxygen,  and  consequently  the  subject  can  endure  a 
lower  oxygen,  which  is  equivalent  to  a  higher  altitude. 

Some  men  have  repeatedly  been  under  observation,  and  most  of 
those  reacted  very  much  the  same  each  time  when  subjected  to  low 
oxygen.  Thus  one  man  who  endured  low  oxygen  unusually  well  in 
a  series  of  seven  tests  averaged  an  increase  of  6.5  liters  in  his  breath- 
ing when  breathing  7  per  cent  of  oxygen.  Another  subject,  who 
invariably  suffered  when  under  the  influence  of  low  oxygen,  in  a 
series  of  five  tests  during  a  period  of  eight  days  had  an  average 
increase  of  only  3.3  liters  in  lung  ventilation. 

When  the  per  minute  volume  of  breathing  fails  to  increase  as  the 
amount  of  oxygen  inhaled  decreases,  or  when  it  increases  only 
slightly — 1  or  2  liters — the  lung  ventilation  is  sufficient  and  the 
subject  will  be  found  unable  to  tolerate  as  low  a  tension  of  oxygen 
as  the  man  whose  breathing  gradually  deepens  as  the  available  oxy- 
gen decreases.  Only  a  few  men  have  failed  to  show  a  respiratory 
response  to  low  oxygen,  and  none  of  these  have  tolerated  well  such 
low  oxygen  as  10  to  9  per  cent.  Men  whose  respiratory  center  is 
insensitive  to  oxygen  want  either  fail  to  show  an  increase  in  the 
breathing  or  are  slow  in  doing  so,  and  in  either  case  there  would  be 
poor  toleration  of  high  altitudes. 

An  occasional  subject  has  been  examined  whose  breathing  re- 
sponded well  at  first,  but  later,  when  the  percentage  of  oxygen  was 
low,  suddenly  began  to  breathe  less.  When  this  happened  fainting  or 
unconsciousness  quickly  followed.  One  subject  in  three  tests  sepa- 
rated by  intervals  of  several  days  suddenly  showed  a  decrease  in  his 
breathing  when  at  10  per  cent  of  oxygen.  He  fainted  the  first  time 
and  was  only  saved  from  doing  so  the  others  by  being  returned  at  once 
to  atmospheric  air.. 

THE  CIRCULATION  WHEN  UNDER  A  DECREASING  OXYGEN  SUPPLY. 

The  rate  of  flow  and  the  amount  of  oxygen  passing  from  the  blood 
to  the  tissues  depends  on  the  difference  between  the  pressure  of  oxygen 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  43 

in  the  blood  and  in  the  tissue.  The  higher  the  oxygen  pressure  in  the 
blood  the  greater  will  be  the  amount  of  oxygen  passing  from  the 
blood  of  the  capillaries  into  the  tissues.  In  active  tissues  the  oxygen 
tension  is  always  low.  It  is  usually  supposed  that  there  is  no  oxygen 
pressure  at  all  inside  the  cells.  The  dissociation  of  oxygen  from  the 
hemoglobin  occurs  with  great  rapidity  and  is  greatest  where  the 
differences  in  pressure  are  greatest.  It  follows,  therefore,  that  when 
the  blood  flows  more  rapidly  through  the  capillaries  of  a  tissue  more 
oxygen  will  be  made  available  than  if  it  flows  slowly.  At  high  alti- 
tudes, or  under  low  oxygen,  the  blood  is,  at  first  at  least,  less  saturated 
with  oxygen  than  at  low  altitudes.  Therefore,  if  the  blood  contains 
less  oxygen  an  increase  in  the  rate  of  blood  flow  through  the  capil- 
laries would  be  a  means  of  providing  the  tissues  with  the  oxygen  de- 
manded for  their  activity.  An  increased  rate  of  blood  flow  has  been 
demonstrated  in  men  living  at  high  altitudes  and  is  undoubtedly  one 
of  the  first  of  the  adaptive  or  compensatory  changes  observed  in  the 
rapid  ascents  made  by  the  aviator. 

Circulatory  observations  made  on  Pike's  Peak  (14,110  feet)  indi- 
cated that  the  increase  in  the  rate  of  blood  flow  was  the  result  of  a 
greater  frequency  of  heart  beat  and  a  dilatation  of  the  arterioles. 

A  study  of  the  pulse  rate  during  exposure  to  low  oxygen  should, 
therefore,  give  a  definite  indication  of  the  sensitiveness  of  the  organ- 
ism to  low  oxygen.  We  have  found  the  pulse  rate  to  be  a  trustAvorthy 
indicator  of  oxygen  want  provided  care  is  taken  at  the  beginning  of 
a  low  oxygen  or  rebreathing  experiment  to  have  the  subject  calm  and 
quiet.  Excitement  or  anxiety  may  give  a  higher  initial  pulse  rate, 
which  will  obscure  the  beginning  of  the  oxygen  want  response. 

Throughout  the  rebreathing  test  the  candidate's  pulse  is  counted 
for  a  period  of  20  seconds  each  minute.  The  systolic  and  diastolic 
blood  pressures  are  determined  every  other  minute  during  the  first 
part  of  the  test  and  every  minute  after  the  oxygen  has  been  reduced 
to  approximately  11  per  cent.  The  rate  of  heart  beat  has  been  found 
to  accelerate  in  a  few  men  at  17.5  per  cent  oxygen  (5,000  feet).  In 
one  group  of  70  men  the  accelerations  began  as  follows :' 

1  per  cent  began  to  react  between  7,000  and  8,000 

feet 16. 0-15.  5  per  cent  oxygen. 

12  per  cent  began  to  react  between  8,000  and  9,000 

feet 15.  5-14. 9  per  cent  oxygen. 

20  per  cent  began  to  react  between  9,000  and  10,000 

feet 14. 9-14. 2  per  cent  oxygen. 

14  per  cent  began  to  react  between  10,000  and  11,000 

feet 14. 2-13.  7  per  cent  oxygen. 

23  per  cent  began  to  react  between  11,000  and  12,000 

feet 13.  7-13. 2  per  cent  oxygen. 

20  per  cent  began  to  react  between  12,000  and  13,000 

feet 13. 2-12. 7  per  cent  oxygen. 

6  per  cent  began  to  react  between  13,000  and  14,000 

feet  _.  12. 7-12. 2  per  cent  oxygen. 


44 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


Legend 


•  Resp.  in  decil.  per  min.  • — •  Syst.  B.  P 

Accom.  in  mm.  Convergence  in  mm. 


- '  »  0  1  a  3  4  5  6  7  8  8  10  11  12  13  14  15  18  17  18  19  20  21  22  23  24  25  20  2t  28  20  30  31  32  33 


TIME  IN  MINUTES 


No.  155.— H.  F.  D.  K. 


CHART  2. 


CADET. 


Age  25  years,  10  months. 


This  is  almost  a  record  run  for  low  percentage  reached,  and  preservation  of  efficiency 
practically  unimpaired  until  the  very  last.  Pulse  rather  high  from  the  start,  as  is  often 
the  case  in  subjects  who  compensate  particularly  well,  and  both  pulse  and  blood  pres- 
sure show  some  psychic  influence  at  the  start.  During  the  course  of  the  test  there  is  a 
typical  moderate  rise  in  pulse  and  systolic  pressure  and  a  gradual  tendency  downward 
of  the  diastolic  pressure.  No  suggestion  of  circulatory  exhaustion.  Bated  AA,  a  par- 
ticularly good  subject. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  45 

The  increase  in  heart-beat  frequency  is  at  first  slight,  only  from  one 
to  three  beats,  but  as  the  oxygen  percentage  decreases  a  greater  in- 
crease in  rate  is  likely  to  occur  with  each  decrement  in  oxygen.  A 
very  marked  acceleration  usually  occurs  when  the  oxygen  has  fallen 
to  between  13  and  9  per  cent.  In  some  men  after  the  beginning  of 
the  more  rapid  increase  in  acceleration  a  steady  increase  in  rate  occurs 
down  to  even  6.5  or  6  per  cent  oxygen,  while  in  others  after  a  period 
of  rapid  acceleration  the  amount  of  acceleration  becomes  less  with 
each  decrease  of  1  per  cent  in  oxygen.  The  last  condition  suggests 
that  the  power  to  compensate  has  about  reached  its  maximum.  Some 
men  at  first  react  with  a  good  acceleration  in  rate  but  soon  reach  a 
rate  beyond  which  there  will  be  no  further  response,  even  though  the 
oxygen  percentage  continues  to  be  lowered.  In  such  cases  after  hold- 
ing at  a  fixed  rate  for  a  while  the  heart  suddenly  begins  to  slow,  a 
sure  indication  that  the  limit  of  endurance  has  been  reached. 

A  total  increase  of  from  15  to  40  beats  in  the  heart  rate  during  a 
rebreathing  test. in  which  the  oxygen  is  lowered  to  between  7.5  and 
6.5  per  cent  constitutes  a  good  reaction  to  oxygen  want.  A  failure  to 
respond  by  an  acceleration  in  heart  beat  to  lowered  oxygen  either 
means  inability  to  react  to  the  low  oxygen  of  high  altitudes  and  early 
failure  or  it  may  mean  that  sufficient  compensation  is  secured  by 
increased  breathing  or  blood  concentration,  or  both.  Our  experience 
indicates  that  the  failure  to  respond  is  associated  with  poor  toleration 
of  low  oxygen.  An  acceleration  in  heart  rate  of  more  than  40  beats — 
50  to  70  have  been  observed — throws  too  great  a  burden  on  the  circu- 
latory mechanism  and  occurs  only  in  men  who  do  not  tolerate  well 
low  percentages  of  oxygen.  In  such  men  other  compensatory  reac- 
tions may  fail  to  occur.  So  far  as  the  response  in  pulse  rate  to  de- 
creasing oxygen  is  concerned  it  therefore  becomes  possible  to  rate  the 
reactions  as  poor,  good,  and  excessive.  A  poor  or  an  excessive  heart 
response  should  disqualify  the  candidate  for  very  high  altitudes;  he 
should  only  ascend  to  moderate  heights. 

A  delay  in  the  first  appearance  of  acceleration  of  the  heart  rate 
may  be  due  to  an  insensitive  cardiac  brain  center  and  an  early  re- 
sponse may  indicate  a  mechanism  very  sensitive  and  responsive  to 
any  decrease  in  available  oxygen.  It  should  be  borne  in  mind,  how- 
ever, that  while  ordinarily  there  is  an  early  acceleration  in  the  heart 
rate,  a  delay  may  be  due  to  the  efficiency  of  other  methods  of  com- 
pensating to  the  stimulus  of  oxygen  want. 

The  determination  of  systolic  and  diastolic  arterial  blood  pressures 
show  whether  the  vasomotor  mechanism  responds  to  the  stimulus  of 
oxygen  want  in  an  adequate  manner  for  maintaining  the  increase  in 
the  rate  of  blood  flow  and  at  the  same  time  whether  the  heart  is  com- 
pelled to  work  against  an  increased  resistance.  They  further  give  an 
index,  the  pulse  pressure,  of  the  volume  of  ventricular  output. 


46  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

COLOR  CHANGES  DURING  REBREATHING. 

The  skin-color  changes  also  give  a  satisfactory  means  of  judging 
the  reaction  of  the  subject  to  low  oxygen.  The  normal  condition  is  a 
gradual  development  of  cyanosis.  In  a  healthy  reaction  this  is  de- 
layed in  its  onset ;  in  a  poor  case  it  appears  early  and  becomes  much 
more  pronounced  as  rebreathing  continues.  Some  men  do  not  show 
a  well-defined  cyanosis  but  become  pale  and  deathlike  in  color.  This 
is  not  a  good  reaction  and  may  be  found  associated  with  other  symp- 
toms— heart  and  circulatory — which  disqualify  for  high  altitudes. 

THE  DURATION   OF  THE  REBREATHING  TEST. 

The  length  of  time  taken  to  reach  a  low  oxygen  in  the  rebreathing 
test  will  profoundly  alter  the  ability  to  endure  extremely  low  per- 
centages. If  the  oxygen  is  lowered  rapidly  the  candidate  compen- 
sates to  a  lower  percentage  than  is  possible  where  the  rate  of  decrease 
in  the  oxygen  is  slower.  Three  rebreathing  experiments  made  on  the 
same  subject  illustrate  the  condition.  The  volume  of  air  was  so  small 
for  the  first  test  that  in  23^  minutes  the  oxygen  was  lowered  to  6.3 
per  cent,  at  which  the  subject's  power  of  compensation  failed.  The 
next  day  rebreathing  a  larger  volume  of  air  for  38  minutes  he  com- 
pensated to  7  per  cent  only.  On  the  following  day  in  a  test  of  85 
minutes'  duration,  compensation  failed  at  8.7  per  cent  of  oxygen. 
Individual  differences  will  be  found;  in  some  men  time  has  a  more 
profound  influence  than  in  others.  Thus  another  subject  compen- 
sated in  a  test  of  36  minutes  down  to  7.5  per  cent  and  in  one  of  90 
minutes  to  8  per  cent  of  oxygen.  Therefore,  when  testing  ability  to 
endure  low  oxygen,  some  allowance  must  be  made  for  the  time  taken 
to  reach  a  given  percentage.  If  each  of  two  men  tolerate  down  to  7 
per  cent  oxygen  but  one  is  carried  down  in  20  and  the  other  in  40  min- 
utes, the  one  who  endures  for  40  minutes  will  have  the  better  power  of 
compensation. 

Control  tests  have  been  conducted  in  the  pneumatic  or  low-pressure 
chamber  to  determine  the  reliability  of  the  rebreathing  test.  A  sub- 
ject was  first  under  observation  in  a  rebreathing  test  and  again  on  the 
following  day  taken  into  the  low-pressure  chamber  for  similar  ob- 
servations, while  the  pressure  was  lowered  at  the  same  rate  that  the 
oxygen  had  been  absorbed  in  the  rebreathing  test.  The  breathing, 
pulse  rate,  and  blood  pressures  reacted  about  the  same  in  each  experi- 
ment. In  order  that  a  comparison  might  be  made  of  the  breathing 
under  the  two  conditions,  the  alveolar  air  was  analyzed  from  time  to 
time  during  each  kind  of  test.  A  fall  in  the  alveolar  carbon  dioxide 
and  oxygen  pressure  occurred  in  both  experiences.  The  average 
amount  of  fall  for  eight  men  at  the  per  cent  of  oxygen  or  pressure 
corresponding  to  20,000  feet  was  for  carbon  dioxide  during  rebreath- 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  47 

ing  8.5  millimeters  and  low  pressure  9.3  millimeters;  for  the  oxygen 
in  rebreathing  66.2  millimeters  and  low  pressure  68.8  millimeters. 
These  figures  show  itfiat  the  increase  in  the  breathing  and  lung  ventila- 
tion was  about  the  same  under  the  two  different  low-oxygen  experi- 
ences. The  pulse  rate  also  was  found  to  begin  to  accelerate  at  about 
the  same  time  in  each  kind  of  test  and  to  accelerate  in  equal  degree. 
These  and  other  physiological  observations  made  on  men  undergoing 
the  rebreathing  test  or  under  decreasing  atmospheric  pressure  prove 
that  the  same  compensations  are  used  by  the  body  in  each,  and  these 
we  know  are  the  adjustments  made  to  the  influence  of  oxygen  want. 

In  the  optimum  type  of  response  to  the  low  oxygen  of  the  rebreath- 
ing test  the  systolic  pressure  remains  unchanged ;  that  is,  it  holds  on 
a  level,  until  the  oxygen  has  been  lowered  to  between  14  and  9  per 
cent  after  which,  as  the  oxygen  is  further  lowered,  it  gradually  rises, 
or  there  may  occasionally  occur  a  gradual  rise  in  the  systolic  pressure 
beginning  with  the  first  increase  in  heart  rate  (see  chart  3).  This 
rise  in  pressure  is  ordinarily  to  from  15  to  20  mm.  Hg.  Other  sub- 
jects who  appear  to  have  tolerated  low  oxygen  well,  even  to  as  low  as 
6.5  per  cent  of  oxygen,  have  had  a  systolic  pressure  which  held  at  the 
normal  (see  chart  2). 

A  rise  in  the  systolic  pressure  of  more  than  30  mm.  Hg. — 40  to  60 
mm.  have  been  observed — is  very  likely  due  to  a  vasomotcr  failure  to 
respond  with  a  dilatation  of  the  arterioles.  Such  conditions  will  lead 
to  overwork  by  the  heart  and  may  result  in  early  circulatory  failure. 

There  are  other  conditions  of  systolic  pressure  that  are  occasionally 
found  in  men  undergoing  the  rebreathing  test.  A  small  percentage 
of  subjects  examined  had  a  fall  in  the  systolic  pressure  which  began 
about  the  time  the  pulse  rate  started  to  accelerate  and  continued  to  de- 
cline throughout  the  test.  Such  men  have  not  tolerated  the  extremely 
low  percentages  of  oxygen  that  men  of  the  optimum  type  of  response 
have  endured. 

A  large  percentage  of  subjects  have  shown  a  sharp  and  sudden  fall 
in  the  systolic  pressure  at  low  percentages  of  oxygen.  This  fall  if 
allowed  to  continue  will  lead  to  fainting.  The  subject  recovers  his 
normal  pressure  at  once  if  he  is  returned  to  atmospheric  air. 

The  best  condition  in  the  response  of  the  diastolic  pressure  to  a  de- 
creasing oxygen  supply  consists  in  an  unchanged  or  slightly  increased 
pressure  throughout  the  test.  Many  men  show  a  gradual  well-con- 
trolled fall  in  the  diastolic  pressure  (see  charts  5  and  6)  during  the 
terminal  period  when  the  systolic  pressure  is  rising.  Such  a  fall  in 
the  diastolic  pressure  if  it  occurs  slowly  and  is  not  great  constitutes  a 
fairly  good  reaction  to  extreme  oxygen  want  and  can  be  explained  as 
a  vasomotor  dilatation  which  occurs  In  order  to  protect  the  heart 
against  the  rising  systolic  pressure.  In  the  optimum  type  of  response 
to  low  oxygen  the  terminal  fall  in  the  diastolic  pressure  may  not 


48 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


Legend  —~O..% 

-»   Diast.  B.  P. 


• — •  ast.      .      .                           u 

200 

|^,; };--(-— :j  ! -  LLulflj-jli.: j. IIJ  .yr 

190  Bi  fer-rinH^ 


Pulse  • --•   Resp.  in  decil.  per  min.         ••••••     Syst.  B.  P 

Pulse  Pressure  Accom.  in  mm..  Convergence  in  mm. 


ISO 


170  igi-M 


TTl'':.:i:  ;:!J'~lT»r"l7  ":. 


a  34  56  7  8  9  10  11  12  IS  14  15  16  17  18  19  HO  21  32  23  24  25  26  27  28  29  30  31  32  : 


TIME  IN  MINUTES 


No.  50.— E.  O.  T.,  2d  Lieut. 


CHAET  3. 

PILOT. 


Age  31  years  8  months. 


In  good  health,  but  "  out  of  training  "  and  20  pounds  overweight. 

This  chart  shows  almost  total  failure  to  compensate.  There  is  very  little  change  in 
pulse  or  blood  pressure,  and  the  respiratory  reaction  is  deficient.  For  this  reason  there  is 
parly  appearance  of  inefficiency  as  shown  by  the  psychological  characters,  and  he  is 
"  completely  inefficient "  above  9  per  cent.  Since  there  is  no  circulatory  reaction,  there 
Is  no  evidence  of  strain.  Class  C.  "  Becomes  inefficient  at  a  relatively  low  altitude." 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  49 

occur,  and  if  present  is  never  very  pronounced  and  does  not  occur 
before  the  oxygen  is  reduced  to  9.5  per  cent  or  less. 

About  66  per  cent  of  all  men  examined  have  had  a  fall  in  the 
diastolic  pressure.  At  least  half  of  these  have  been  sudden  and  great. 
The  rapid  fall  is  always  associated  with  fainting,  and  usually  precedes 
a  systolic  fall.  If  the  two  occur  together,  in  the  order  just  indicated, 
the  experiment  must  be  terminated  at  once  if  fainting  is  to  be  pre- 
vented. The  pronounced  and  sudden  fall  in  diastolic  pressure  may 
occur  at  a  high  oxygen  percentage.  It  has  been  found  to  occur  as 
early  as  14  and  13  per  cent  of  oxygen  (10,400  and  12,200  feet).  Such 
sudden  falls  in  the  diastolic  pressure  appear  to  be  due  to  an  over- 
coming of  the  vasomotor  center  by  oxygen  shortage.  A  decided  fall 
in  the  diastolic  pressure  even  if  more  or  less  definitely  controlled  is  an 
indication  that  the  subject  will  not  tolerate  well  the  altitude  corre- 
sponding to  the  oxygen  percentage  at  which  it  appears. 

Three  types  of  circulatory  reaction  to  oxygen  want  have  been  ob- 
served. The  first,  the  optimum,  in  which  the  pulse  rate  accelerates 
moderately  as  the  oxygen  decreases,  the  systolic  pressure  is  un- 
changed or  shows  a  terminal  rise  of  not  more  than  20  to  30  mm.  Hg., 
and  the  diastolic  pressure  remains  unchanged  or  rises  slightly  (see 
chart  2).  The  second,  the  controlled  diastolic  fall,  in  which  the 
pulse  rate  accelerated  moderately  and  the  systolic  pressure  rises 
as  the  diastolic  pressure  gradually  falls  (see  charts  3  and  6).  The 
third,  the  fainting  type  (see  charts  I  and  4),  in  which  after  a  period 
of  fair,  good,  or  excessive  response  in  the  rate  of  heart  beats  to  low 
oxygen  the  diastolic  pressure  suddenly  falls  and  soon  thereafter  the 
systolic  pressure  falls  and  the  pulse  rate  slows.  The  optimum  type 
may  tolerate  as  low  an  oxygen  as  6  per  cent  and  may  lose  con- 
sciousness without  fainting.  He  recovers  quickly  when  restored  to 
air,  while  the  heart  rate  and  blood  pressures  are  soon  back  to  their 
normals.  The  fainting  type  rarely  endures  as  low  an  oxygen  and 
if  allowed  to  run  his  course  faints  completely,  and  as  he  revives  he 
requires  a  considerable  time,  sometimes  an  hour  or  two,  to  regain  his 
normal  pulse  rate  and  blood  pressures.  There  are,  of  course,  grada- 
tions between  the  types  here  described. 

The  pulse  pressure  during  a  rebreathing  test  remains  fairly  con- 
stant in  most  men  until  the  oxygen  has  fallen  to  between  12  and  9 
per  cent  (14,500—22,000  feet),  after  which  it  increases  in  amount 
during  the  further  reduction  in  oxygen.  The  rise  in  pulse  pressure 
occurs  when  the  systolic  pressure  is  rising  and  the  diastolic  either 
remaining  constant  or  slowly  falling.  This  is  also  the  period  when 
the  heart  beat  is  accelerating  most  rapidly.  The  amplitude  of  the 
heart  output,  it  is  claimed,  is  shown  by  the  pulse  pressure;  if  the 

89119—18 4 


50  MANUAL  Or   MEDICAL  EESEAECH   LABOKATOBY. 

pulse  pressure  be  multiplied  by  the  pulse  rate  and  the  product  be 
taken  as  a  relative  measure  of  the  volume  of  the  blood  stream  and 
increase  in  the  circulation  rate  will  be  indicated,  beginning  between 
16  and  14  per  cent  of  oxygen  and  progressively  increasing  as  the 
oxygen  further  decreases.  The  period  of  most  rapid  flow  of  blood 
Avould,  therefore,  be  that  when  the  pulse  pressure  is  also  increasing, 
that  is,  from  between  12  and  9  per  cent  of  oxygen  to  the  end  of  the 
test.  Therefore  a  marked  increase  in  the  rate  of  the  circulation  of 
the  blood  during  exposure  to  a  IOAV  and  decreasing  oxygen  is  indi- 
cated. This  increase  in  blood  flow  is,  as  shown  earlier,  an  important 
and  necessary  compensatory  reaction  to  low  oxygen. 

Incidentally  a  few  venous  blood  pressure  determinations  made 
during  exposure  to  a  decreasing  oxygen  supply  have  shown  a  drop 
in  venous  pressure,  which  becomes  very  pronounced  when  the  oxygen 
is  10  per  cent  or  less.  The  following  are  typical  examples : 

1.  Normal  venous  blood  pressure  was  10.8  centimeters  of  blood. 
After  25  minutes,  during  which  time  the  oxygen  was  gradually  de- 
creased to  8  per  cent,  it  had  fallen  to  3.5  centimeters  of  blood.    Re- 
turned to  normal  within  five  minutes  after  being  returned  to  air. 

2.  Normal  venous  pressures  9  centimeters;  20  minutes  later  at  10 
per  cent  oxygen,  3.5  centimeters.    Return  to  normal  after  experiment 
required  15  minutes. 

3.  Normal,  6.6  centimeters;  fell  to  5  centimeters  in  30  minutes  when 
the  oxygen  had  reached  7.5  per  cent. 

This  fall  in  venous  pressure  calls  to  mind  a  similar  fall  reported 
by  Schneider  and  Sisco  in  men  on  Pike's  Peak,  and  it  indicates  that 
the  reactions  observed  in  the  rebreathing  tests  are  the  result  of  the 
same  cause — low  oxygen. 

VENOUS  PRESSURE. 

For  the  determination  we  used  a  tilting  table,  which  made  it  easy 
to  study  the  subject  in  the  horizontal  position.  The  subjects  of  our 
studies  were  officers  and  enlisted  men  of  the  laboratory,  presumably 
normal  men. 

Venous  pressure  was  determined  by  noting  the  height  to  which 
the  arm  could  be  lifted  before  some  prominent  bit  of  vein  in  or  near 
the  hollow  of  the  elbow  collapsed,  and  comparing  this  with  the 
height  of  the  point  of  reference  between  these  two  levels,  read  in 
centimeters,  gives  the  venous  pressure  directly  in  centimeters  of 
blood. 

The  point  of  reference  was  taken  as  5  centimeters  below  the  level 
of  the  nipple,  and  this  level  was  carried  away  from  the  breast  by 
means  of  a  simple  spirit  level.  Measurements  were  read  on  a  centi- 
meter rule  suspended  from  the  ceiling. 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 


51 


•  —  -  — -•     Resp.  in  decil.  per  min.     •••...«•••  .Syst.  B.  P 


11  "  0  1  3  3  4.  .5  ,  «.;  7  -  8  .8  10  11  12  13  14  15  16  17  18  19  30  21  23  33  34  25  20  27  28  *»  30  81  82  33 

TIME  IN  MINUTKS 

CHABT  4. 


No.  144.— L.  R.  S. 


CADET. 


Age  20  years,  2  months. 


Is  decidedly  "  stale,"  hates  to  go  up  in  the  air  at  all.  Feels  tired  and  depressed,  and 
is  discontented  in  the  service  at  present.  Certain  complications  at  home  are  on  his  mind 
a  good  deal. 

This  chart  is  typical  of  a  man  in  poor  physical  and  mental  condition.  He  fainted 
rather  suddenly  at  about  13  per  cent.  Previous  to  this  he  had  shown  little  com- 
pensatory response;  blood  pressure  too  low  from  the  start,  pulse  rising  slightly  and 
respiration  hardly  at  all  affected.  This  man  might  be*expected  to  faint  at  any  time 
during  a  flight,  irrespective  of  elevation. 

No  rating  given,  but  for  the  time  being  is  unfit  to  fly  at  all.  Withdrawn  from  flying 
and  recommendation  made  for  furlough. 


52 


MANUAL  OF   MEDICAL  "RESEARCH   LABORATORY. 


The  data  on  the  venous  pressure  study,  though  meager  as  yet,  are 
sufficient  to  show  that  with  an  increase  of  altitude  there  is  a  decrease 
in  venous  pressure.  This  change  in  venous  pressure  shows  great 
individual  variations,  ranging  from  4.1  per  cent  to  104  per  cent 
drops.  Only  one  case  showed  a  final  rise  in  venous  pressure.  After 
a  drop  from  8.3  centimeters  of  blood  to  5.3  centimeters  of  blood  the 
pressure  started  to  rise  and  continued  to  rise  until  the  end  of  the 
experiment. 

Out  of  nine  cases,  the  one  mentioned  above  was  the  only  one  that 
did  not  show  a  lowered  venous  pressure  under  decreased  oxygen. 
In  many  cases  the  pressure  showed  a  tendency  to  decrease  with  the 
first  indications  of  lowered  oxygen  percentage.  Others  did  not 
respond  until  the  oxygen  had  reached  about  13  per  cent  to  14  per 
cent,  after  which  the  pressure  dropped  quite  abruptly  to  the  end  of 
the  experiment. 

From  eight  cases  studied  with  the  Dreyer  apparatus,  the  following 
data  were  compiled: 


i 

Normal 
V.  P. 

Fall  in 
V.  P. 

Per  cent 
fall. 

Oj. 

1                               

Cm.  blood. 
8.75 

Cm.  blood. 
9.05 

Per  cent. 
104.0 

Per  cent. 
10.2 

2                                     

6.45 

2.40 

37.2 

7.5 

3.                         

4.48 

.98 

21.8 

8.5 

4  

*    9.70 

6.25 

ti4.  5 

6.6 

2.40 

1.10 

45.8 

10.0 

6                                     

4.03 

2.58 

64.0 

7.3 

7.                             

6.30 

3.50 

55.5 

8.7 

8  

6.88 

.28 

4.1 

8.63 

Average.  .            

6.12 

3.27 

49.6 

8.43 

The  above  studies  bear  out  rather  well  the  findings  of  Schneider 
and  Sisco  in  their  Pike's  Peak  investigations,  and  indicate  that  the 
reactions  observed  in  the  rebreathing  tests  are  the  result  of  the  samo 
cause — low  oxygen. 

THE  RELATION  OF  VITAL  CAPACITY,  POWER  TO  HOLD  THE  BREATH  AND 
ENDURANCE  OF  LOW  OXYGEN. 

The  English  suggest  the  rejection  of  all  candidates  with  a  vital 
capacity  below  3,000  cc.  and  view  with  suspicion  all  belowr  3400  c^. 
The  candidate  also  should  be  able  to  hold  the  breath  a  minimum,  in 
three  times,  oiL4j>  s^cjQjods.  They  find  that  good,  pilots  manage  60 
seconds  or  more.  If  dizziness,  blurred  vision,  etc.,  occur  under  40 
seconds,  they  reject  the  candidate,  no  matter  what  the  vital  capacity 
may  be.  A  further  test  often  applied  is  to  have  the  candidate  hold 
the  breath  after  the  moderate  exercise  of  stooping  and  touching  the 
floor  four  times.  After  'the  exercise  the  candidate  should  be  able  to 
hold  the  breath  30  seconds.  Good  pilots  hold  at  least  40  seconds,  gen- 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


53 


erally  between  50  and  60  seconds.  None  of  the  men  examined  by  us 
had  a  vital  capacity  less  than  3,400  cc.  Four  who  were  unable  to 
endure  a  low  percentage  of  oxygen  in  the  rebreathing  experiments 
had  vital  capacities  ranging  between  4,400  and  5,000  cc.  In  view  of 
our  observations  it  appears  that  the  vital  capacity  does  not  serve  as 
an  index  for  the  approximation  of  the  limits  of  endurance  of  low 
oxygen  (see  following  table  prepared  from  observation  on  50  men). 


Subject. 

Vital 
capacity. 

Holding  of  breath. 

Lowest 
per  cent 
of  oxygen 
endured. 

Danger  percentage. 

Before 
exercise. 

After 
exercise. 

An... 

4,200 
5,000 
4,600 
3,800 
4,500 
4,350 
4,400 
3,800 
5,200 
4,500 
•4,750 
4,700 
3,650 
4,200 

Seconds. 
40 
75 
80 
47 
107 
72 
60 
76 
56 
62 
75 
60 
62 
29 

Seconds. 
24 
50 
58 
38 
34 
57 
54 
40 
57 
30 
74 
24 
32 
20 

Per  cent. 
6.8 
8.4 
9.2 
6.6 
9.8 
7.2 
6.8 
8.8 
6.3 
7.3 
6.3* 
6.7 
8.2 
7.3 

Not  reached. 
10. 
9.2. 
8.3. 
11.3. 
11.3. 
Not  reached. 
10. 
6.3. 
10.3. 
7.7. 
8. 
8.2. 
Not  reached. 

Br  

Be  

Cl  

Fin  

Per  

(Jin... 

Kr  

Par..  . 

Roc... 

Sen  

Snv  

Tr.... 

W  

An.,  with  a  vital  capacity  less  than  that  of  Br.,  Be.,  and  Fin.,  had 
not  completely  reached  the  limit  of  endurance  at  6.8  per  cent  (28,400 
feet),  while  Br.  failed  at*  8.4  per  cent  (24,000  feet),  Be.  fainted  at 
9.2  per  cent  (21,800  feet),  and  Fin.  at  9.8  (20,000  feet).  Compare 
the  last  three  with  Cl.,  whose  vital  capacity  was  only  3,800  cc.,  and 
who  endured  low  oxygen  down  to  6.6  per  cent. 

The  length  of  time  the  breath  was  held  did  not  give  an  indication 
of  how  lolv  in  oxygen  the  subject  would  go  on  the  rebreathing  appa- 
ratus. Fin.  and  Be.,  who  fainted  at  9.8  per  cent  (20,000  feet)  and 
9.2  per  cent  (21,800  feet),  respectively,  held  the  breath  longer  than 
the  average.  An.,  who  managed  only  40  seconds,  withstood  6.8  per 
cent  oxygen  (28,400  feet),  and  W.,  who  held  only  29  seconds,  endured 
low  oxygen  down  to  7.5  per  cent  (26,000  feet). 

VITAL  CAPACITY  AND  INTESTINAL  GASES  AT  HIGH  ALTITUDES. 

That  vital  capacity  of  the  lungs  decreases  with  lowering  atmos- 
pheric pressure  has  long  been  established  by  investigations  carried 
on  in  this  country  and  abroad.  The  cause  of  the  decreased  vital 
capacity  at  high  altitudes  has  not,  however,  been  wholly  determined 
That  oxygen  want  plays  a  part  in  this  as  well  as  in  other  physiologic 
low-pressure  symptoms  seems,  from  our  investigations,  to  be  prac- 
tically certain.  That  oxygen  want  alone  is  not  wholly  responsible 
seems  equally  certain. 


54  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

For  our  investigations  we  used  a  simple  water  spirometer  with  a 
capacity  of  about  7  liters.  The  work  was  done  in  the  low-pressure 
chamber  under  conditions  simulating  those  encountered  at  altitudes 
ranging  between  sea  level  and  22,000  feet. 

First  a  series  of  observations  was  made  in  which  the  subjects  were 
taken  to  20,000  feet,  without  oxygen,  to  determine  the  amount  of 
decrease  in  vital  capacity.  In  17  cases  the  average  decrease  was 
0.48  liter  (approximately  10  per  cent),  the  maximum  1.08  liters  (25 
per  cent),  and  the  minimum  0.15  liter  (3  per  cent).  A  well-defined 
decrease  does  not  occur  below  10,000  feet;  the  majority  of  men  seem 
to  hold  on  well  to  12,000  to  14,000  feet.  In  this  connection  it  is  inter- 
esting to  note  that  three  men  who  have  lived  most  of  their  lives  at 
altitudes  above  5,000  feet  retained  their  normal  vital  capacity  to 
greater  altitudes  than  did  the  men  who  had  always  lived  at  low  alti- 
tudes. In  one  the  first  break  came  at  14,000  feet,  the  second  held  to 
16,000  feet,  and  the  third  was  still  normal  at  18,000  feet.  On  the 
other  hand,  several  whose  homes  had  been  at  less  than  1,000  feet 
showed  a  decreased  capacity  at  10,000  feet. 

.  A  second  series  was  run  in  which  the  subjects  took  oxygen  through- 
out the  experiment,  and  in  this  series  there  also  occurred  a  decrease 
in  vital  capacity.  In  six  cases,  going  from  sea  level  to  20,000  feet, 
the  average  decrease  in  vital  capacity  was  0.20  liter,  or  4.5  per  cent 
below  normal. 

A  number  of  men  were  taken  to  20,000  feet  without  oxygen.  At 
that  altitude  they  were  given  oxygen  and  held  a  sufficient  length  of 
time  for  the  oxygen  to  effect  the  system.  The  usual  decrease  to  20,000 
without  oxygen  was  observed.  When  oxj^gen  was  administered  a 
definite  and  unmistakable  return  toward  the  normal  was  noted,  but 
in  no  case  did  the  readings  at  20,000  feet  equal  the  normal  readings 
at  sea  level.  In  a  study  of  six  cases  the  following  data  were  obtained : 

Average  V.  C.  at  sea  level 4.  45 

Average  V.  C.  at  20,000  feet  without  Oa 3.  94 

Average  V.  C.  at  20,000  feet  after  taking  O2 4.  23 

That  the  aviator  may  be  distressed  by  an  abdominal  bloating  due 
to  expansion  of  gases  in  the  intestine  during  an  ascent  has  been  sug- 
gested. The  gases  accumulated  in  the  digestive  organs  expand  as 
the  external  pressure  falls  so  that  at  18,000  feet — that  is,  half  an 
atmosphere  of  pressure — the  gases  in  the  digestive  organs  will  expand 
to  double  their  volume.  This  may  lead  to  an  unpleasant  pressure  on 
the  abdominal  wall  and  diaphragm  and  this,  it  has  been  suggested, 
might  cause  difficulty  in  breathing  by  forcing  up  the  diaphragm  and 
thus  decreasing  the  space  of  the  thoracic  cavity.  When  gas  forms 
continually  in  the  digestive  organs  in  consequence  of  a  diet  rich  in 
carbohydrate  foods,  such  as  sugars,  green  vegetables,  and  others  that 
are  easily  fermented,  the  decrease  in  vital  capacity  might  be  expected 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


55 


Legend  .. 


«— •— -.  Diast.  B 


.  .Puis«.  • — •---< 

Pulse  Pressure 


Resp.  in  decil.  per  min. 
Accom,  in  mm." 


•....*... -»Syst.  B.  P 
Convergence  in  mm. 


10    11    12    13    14    15    16    17    18    1»   30    21    32   23 


0     1     8     3 
TIME  IN  MINUTES 


4    5 


No.  352.— R.  P.  E. 


CHABT  5. 


CADET. 


Age  22  years,  1  months. 


Preliminary  blood  pressures :  Reclining,  134 ;  standing,  142 ;  after  exercise,  160 ;  two 
minutes  later,  134. 

During  the  test  has  a  high  and  gradually  increasing  systolic  pressure.  Diastolic 
comes  down  rather  steeply  after  20  minutes  (10  per  cent),  though  never  out  of  control. 
Pulse  and  respiration  normal.  Marked  psychic  effects  soon  after  diastolic  pressure  be- 
gins to  fall.  High  blood  pressure,  with  signs  of  fatigue,  but  candidate  in  class  C  in 
spite  of  his  reaching  a  fairly  low  percentage  before  the  actual  break. 


56  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

to  be  greater  than  in  the  man  in  whom  little  or  no  fermentation  is 
occurring.  Careful  study  of  this  condition  failed  to  establish  any 
relation  between  abdominal  bloating  and  the  decrease  in  vital 
capacity  during  experiments  in  the  low-pressure  chamber.  It  was 
found  that  the  abdominal  measurements  may  vary  greatly  at  any 
single  pressure  while  the  vital  capacity  remains  constant.  Belching 
or  otherwise  releasing  the  digestive  gases  reduced  the  abdominal 
measurements  and  materially  relieved  the  distress  of  the  subject 
without  causing  any  noticeable  change  in  the  vital  capacity. 

The  decrease  in  vital  capacity  of  the  lungs  appears,  therefore,  to  be 
largely  due  to  the  oxygen  want  of  high  altitudes  and  not  to  be  caused 
by  the  pushing  up  of  the  diaphragm  by  the  expanding  gases  of  the 
intestines. 

VASOMOTOR  TONE  AND  ENDURANCE  OF  LOW  OXYGEN. 

Since  physical  fitness  has  been  found  to  influence  profoundly  the 
ability  of  men  to  endure  low  oxygen  it  was  thought  that  Crampton's 
"blood  ptosis  test"  might  be  used  to  approximate  the  altitude  the 
aviator  could  tolerate.  The  vasomotor  mechanism  is  easily  wearied 
and  damaged  by  unhygienic  influences.  The  fact  that  the  vasomotor 
control  of  the  splanchnic  area  in  man  experiences  a  change  of  adjust- 
ment when  the  body  is  moved  from  the  horizontal  to  the  upright- 
standing  position  has  been  used  by  Crarnpton  to  devise  a  percentage 
scale  of  vasomotor  tone  for  rating.  In  vigorous  subjects  the  heart 
rate  does  not  increase  on  standing  but  in  wearied  subjects  it  increases 
as  much  as  44  beats  per  minute.  In  a  perfectly  strong  subject  the 
splanchnic  vasotone  will  increase  on  standing  and  raise  the  systolic 
blood  pressure  about  10  millimeters  of  Hg.  while  in  an  individual 
weakened  by  dissipation,  overwork,  or  lack  of  sleep  the  pressure  will 
tend  not  to  rise  but  to  fall.  To  estimate  the  vasomotor  tone  the  pulse 
rate  and  the  systolic  pressure  are  determined  on  a  subject  after  re- 
clining five  minutes  and  again  after  he  is  required  to  stand.  &  sub- 
ject sometimes  may  show  weakness  by  a  decrease  in  blood  pressure 
and  at  other  times  by  an  increase  in  heart  rate,  and  vice  versa.  It 
was  determined  that  a  decrease  of  one  millimeter  of  mercury  was 
equivalent  to  an  increase  in  heart  rate  of  approximately  two  beats. 

A  study  of  130  aviators  in  which  the  vasomotor  tone  index  was 
compared  with  the  physiological  compensatory  reactions  during  ex- 
posure to  the  influence  of  the  low  oxygen  of  the  rebreathing  test  has 
shown  that  Crampton's  vasomotor  tone  index  does  not  give  a  reliable 
indication  of  the  subject's  ability  to  withstand  low  oxygen  tensions. 
When  the  candidates  are  arranged  in  the  four  groups  of  our  scheme 
for  classifying  aviators  the  AA  group  has  an  average  vasomotor  tone 
of  88.75,  the  A's  68.25,  the  B's  57,  and  the  C's  68.13.  Collectively, 
therefore,  the  vasomotor  tone  index  appears  to  furnish  information 


MANUAL  OF   MEDICAL  RESEARCH  LABORATORY. 


57 


Legend 


6,% 

• JDiast.  B,  P. 


*  Pulse  •- 

Pulse  Pressure 


»Resp.  in  decil.  per  min.          • «6yst.  B.  P 

Accom.  in  mm.  Convergence  in  mm. 


«     n    n     o     1     23     4     5     6     1    18     9    10    11    12   13   14  15    18  IT   IS   19  20   21    2i   23   21@5   20  27  28  29   30  81   32   83 

TIMTT  IK  MINUTES  X 

CHART  6. 
No.  351. — W.  S.    .  Age  20  years  4  months. 

Preliminary,  blood  pressures :  Reclining,  122 ;  standing,  138 ;  after  exercise,  156,  and 
two  minutes  later,  138. 

During  the  test  the  pressure  is  a  little  high  and  trends  upward.  The  diastolic  pressure 
begins  to  fall  rather  rapidly  after  the  nineteenth  minute  (10.5  per  cent),  but  is  never 
out  of  control.  At  the  same  time  systolic  pressure  falls  somewhat  and  the  pulse  fails 
to  advance.  This  is  the  picture  of  circulatory  fatigue,  and  if  pushed  much  longer  col- 
lapse would  follow.  Note  that  marked  psychological  effects  (diamonds)  appear  just  as 
the  circulatory  fatigue  becomes  manifest.  Complete  inefficiency  at  a  rather  high  per- 
centage (8  per  cent).  Class  B. 


58  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

that  might  be  useful  except  for  the  C  group.  The  number  of  men 
in  class  C  is  rather  small,  5  in  all,  so  that  the  chance  for  error  is 
greater.  An  examination  of  the  individual  cases  in  the  four  groups 
shows  clearly  that  the  Crampton  vasomotor  tone  index  can  not  be 
depended  upon  as  a  test  for  ability  to  react  to  low  oxygen.  Thus 
among  the  A's  are  vasomotor  tones  as  low  as  30  and  as  high  as  110, 
among  the  B's  15  and  105.  With  such  a  wide  range  of  variation  it 
becomes  evident  that  the  vasomotor  tone  index  can  not  be  substituted 
for  the  rebreathing  test.  Low  vasomotor  tone  is  no  doubt  present  in 
physically  stale  men,  but  it  also  occurs  in  men  temporarily  fatigued. 

THE  PULSE  RATE  AMD  BLOOD  PRESSURES   AFTER   PHYSICAL   EXERTION. 

It  is  generally  assumed  that  in  vigorous  physically  fit  men  the  rate 
of  heart  beat  does  not  accelerate  as  much  during  a  given  exercise  as 
in  men  out  of  training  and  therefore  physically  "  soft."  Further- 
more, in  the  physically  fit  the  rate  returns  to  normal  quickly,  while 
in  the  less  strong  a  higher  rate  is  maintained  some  time  after  exer- 
cising. After  short  periods  of  exertion  the  pulse  rate  usually  goes 
subnormal,  but  after  fatiguing  and  exhausting  exercise  returns  to 
normal  more  slowly  and  only  rarely  passes  into  the  subnormal  stage.  • 
The  amount  of  increase  in  the.  heart  rate  and  the  time  required  to 
return  to  normal  may  be  used  as  a  measure  of  physical  fitness. 

All  aviators  and  candidates  examined  in  the  Medical  Research 
Laboratories  undergo  the  following  test:  The  candidate  stands  at 
ease  while  his  pulse  rate  is  counted;  when  two  successive  counts  are 
the  same  the  rate  is  recorded,  and  the  arterial  blood  pressures 
immediately  taken.  The  candidate  then  places  his  right  foot  on  a 
chair  and  raises  himself  five  times  to  the  erect  position  on  the  chair. 
This  exercise  requires  about  15  seconds.  Immediately  thereafter  the 
pulse  rate  is  counted  for  20  seconds,  and  next,  as  quickly  as  possible. 
the  arterial  pressures  are  determined.  He  then  stands  at  ease  for 
two  minutes,  after  which  the  pulse  rate  and  pressures  are  again 
taken. 

An  analysis  of  170  cases  taken  at  random  has  been  made  and  com- 
parisons made  with  the  reaction  of  the  candidate  to  the  low  oxygen  of 
the  rebreathing  test.  Also  a  comparison  with  the  vasomotor  tone  has 
been  made.  The  following  changes  in  pulse  rate  were  obtained 
immediately  after  the  exercise :  Decrease  in  7.1  per  cent,  no  change  in 
7.6  per  cent,  an  increase  of  from  1  to  10  beats  in  38.2  per  cent,  an 
increase  of  from  11  to  20  in  34.1  per  cent,  and  21  to  30  in  13  per  cent. 
Just  what  increase  in  the  rate  of  heart  beat  is  excessive  is  yet  to  be 
determined.  Maj.  Flack  and  Capt.  Bowdler  conclude  for  the  same 
exercise  that  an  increased  rate  of  over  25  and  a  return  period  of  over 
30  seconds  are  points  calling  for  careful  consideration.  Only  6.5 


MANUAL  OF   MEDICAL  RESEARCH   LABOBATOBY.  59 

per  cent  of  our  subjects  had  an  increase  of  over  25  beats.  On  coin- 
paring  the  above  data  with  the  showing  the  men  made  in  ability  to 
compensate  to  the  low  oxygen  of  the  rebreathing  test,  we  find  no 
definite  relationship  indicated  between  the  amount  of  acceleration 
after  exercise  and  endurance  of  low  oxygen.  Neither  do  we  find  a 
relationship  between  the  exertion  pulse  rate  acceleration  and  Cramp- 
ton's  vasomotor  tone  index. 

We  did  not  follow  the  return  of  the  pulse  rate  to  normal  after  ex- 
ercise but  noted  the  rate  two  minutes  after.  The  rate  at  the  end  of 
the  second  minute  was  above  normal  in  33  per  cent,  normal  in  16.8 
per  cent,  and  subnormal  in  50.2  per  cent  of  the  men.  None  of  the 
subjects  had  a  rate  of  over  10  above  normal  at  the  end  of  two  minutes. 
The  number  above  normal  is  certainly  excessive  according  to  the 
standards  of  Flack  and  Bowdler.  In  this  study  no  relationship  could 
be  established  with  the  ability  to  compensate  to  low  oxygen  nor  with 
the  vasomotor  tone. 

The  changes  in  the  systolic  pressure  immediately  after  the  exercise 
show  nothing  definite  as  to  physical  condition  and  as  to  ability  to 
endure  low  oxygen.  The  systolic  pressure  two  minutes  after  exercise, 
when  compared  with  the  pulse  rate  changes,  show  collectively  inter- 
esting differences.  The  group  with  the  pulse  rate  above  normal  had 
Systolic  pressures  above  normal  in  22.8  per  cent  and  below  normal 
in  66  per  cent  of  the  men;  those  whose  pulse  rate  had  returned  to 
normal  showed  68  per  cent  above  and  18  per  cent  below  the  normal 
systolic  pressure;  while  in  those  in  which  the  pulse  rate  was  sub- 
normal 82.1  per  cent  were  above  and  only  7.1  per  cent  below  their 
normal  systolic  pressure.  It  appears,  therefore,  that  when  the  heart 
rate  remains  up  after  exercise  the  systolic  pressure  more  frequently 
becomes  subnormal.  This  observation  has  not  been  found  to  bear 
upon  the  ability  of  men  to  react  to  low  oxygen.  It  does,  however, 
indicate  that  the  vasomotor  tone  index  is  a  more  reliable  method  of 
judging  fatigue  and  possibly  staleness  than  either  a  study  of  the 
pulse  rate  or  systolic  pressure  alone. 

Flack  and  Bowdler  believe  the  ideal  pulse  rate  for  a  flying  officer 
has  a  snlall  range  between  systolic  and  diastolic  pressures  (20-30) 
with  a  rest  rate  increased  20-25  by  exercise  and  returning  to  the 
rest  rate  in  10-15  seconds.  They  further  state  that  a  pulse  of  60  to 
72  little  raised  by  exercise  (10  beats  per  minute)  and  returning  to 
normal  in  10  seconds  is  a  good  sign,  generally  associated  with  excel- 
lent physique  and  good  stability  of  the  nervous  system.  We  have  no 
reason  to  doubt  their"  conclusion  but  believe  the  values  given  may 
be  increased  by  a  good  margin  and  still  retain  the  physical  perfection 
desired.  About  37  per  cent  of  our  subjects  had  when  standing  up- 
right pulse  rates  above  85  and  the  pulse  pressures  of  the  great  ma- 


60 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 


Legend 


Resp.  in  decil.  per  min.  • «Syst.  B.  P 

Convergence  in  mm. 


n.   it    n    o     1     2 
TIME  IN  MINUTES 


4  5  67  8  9  10  11  12  13  14  15  16  17  18  10  SO  21  22  33  24  25  26  27 

Sf 


No.  154.— S.  A.  C. 


CHAET  7. 


CADET. 


Age  23  years  5  months. 


Good  condition. 

This  chart  is  rather  a  curiosity.  It  shows  (aside  from  a,  psychic  rise  at  the  start) 
practically  no  low  oxygen  effect  on  pulse  or  blood  pressure.  There  is  fair  response  in 
respiration.  In  spite  of  this,  the  subject  preserves  his  efficiency  by  the  psychological 
tests  to  a  very  low  percentage,  viz,  6.8  per  cent.  This  is  a  most  unusual  case,  which 
should  be  investigated  further.  There  is  no  doubt  that  he  compensates  in  some  way, 
since  his  efficiency  holds  out  so  well,  but  he  does  not  do  it  in  the  usual  way.  Most 
cases  showing  such  lack  of  response  in  pulse  would  show  early  inefficiency.  Rated  AA. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  61 

jority  ranged  between  30  and  60  mm.  Hg.  They  believe  that  a 
diastolic  pressure  below  70  with  a  pulse  pressure  greater  than  50, 
is  strong  evidence  that  the  cardiovascular  system  is  unsuited  for 
air  work.  About  30  per  cent  of  our  fliers  have  had  when  standing 
a  pulse  pressure  greater  than  50.  The  method  of  taking  the  arterial 
pressures  may  account  for  the  differences  noted.  We  have  used  the 
Tycos  sphygmomanometer  and  taken  the  pressures  with  the  arm  at 
the  side  by  the  auscultatory  method,  the  systolic  pressure  being  read 
at  the  point  of  reappearance  of  the  pulse  and  the  diastolic  pressure 
at  the  point  of  disappearance  of  the  sound. 

In  comparing  our  data  with  the  conclusions  of  Flack  and  Bowdler 
we  find  33  per  cent  of  our  men  had  a  pulse  rate  above  normal  at  the 
end  of  two  minutes.  Without  taking  into  consideration  the  inter- 
play between  pulse  rate  and  systolic  pressure,  it  apparently  would 
not  be  just  to  rule  against  the  subject  because  of  a  slow  return. 

OBSERVATIONS   ON   THE  EFFECTS   OF   FLYING  UPON   THE   PULSE  RATE   AND 
THE  ARTERIAL  PRESSURES. 

The  experiments  were  carried  out  on  the  flying  plateau  immedi- 
ately before  and  after  a  flight.  The  aviator  reclined  for  five  minutes, 
after  which  the  pulse  rate  was  counted  and  the  pressures  then  taken. 
He  next  was  required  to  stand  while  each  was  again  determined.  The 
same  method  of  examination  was  followed  before  and  after  flight. 
Such  observations  are  still  being  continued.  None  of  the  flights  have- 
exceeded  a  height  of  more  than  6,000  feet,  while  the  average  altitude 
attained  varied  between  2,500  and  4,000  feet.  The  duration  of  the 
flight  rarely  exceeded  an  hour.  The  pulse  rate  in  both  postures  was 
found  to  be  more  rapid  after  than  before  the  flight  in  about  60  per 
cent  of  the  men,  was  unchanged  in  20  per  cent,  and  was  decreased 
in  20  per  cent.  The  increase  was  in  several  as  high  as  28  beats  per 
minute.  The  excitement  attending  the  anticipation  of  the  flight  was 
evidenced  in  a  more  rapid  pulse  rate  only  in  men  who  had  but  little 
experience  in  solo  flying  or  had  some  trouble  in  previous  flying. 

The  systolic  pressure  in  both  postures,  reclining  and  standing,  was 
higher  after  than  before  the  flight  in  approximately  75  per  cent  of 
the  men  studied,  20  per  cent  had  a  lower  systolic  pressure  on  the  re- 
turn, while  about  5  per  cent  showed  no  change.  The  amount  of  rise 
above  normal  ranged  from  2  to  34  millimeters  of  mercury.  The 
greatest  fall  was  10  millimeters  of  mercury. 

The  diastolic  pressure  was  in  approximately  56  per  cent  of  the  men 
lower  after  flying  than  before.  In  no  case  was  the  fall  excessive. 

By  balancing  the  systolic  pressure  and  the  heart  rate  for  reclining 
and  standing  postures  to  determine  the  efficiency  of  the  vasomotor 
system  and  rating  the  reaction,  according  to  Crampton's  scale  of 
vasomotor  tone,  we  find  that  the  majority  of  the  aviators  studied  show 


62 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


Legend 


'»—.+         Diast.  B.  P. 


».Resp.  in decifrper  min.     • -••    Syst.  B.  P 

Accom.  in  mm.  Convergence  in  mm. 


10 


*     n    n^  o     13     3     4     5     6     7     8     9    10    11   12   18   14  15    16   17   18   19   20   SI   33   23  34  25   2^27   38  20  3 
TIME  IN  MINUTES 


No.  110.— R.  S. 


CHAET  8. 

CADET. 


Age  35  years  11  months. 


This  chart  is  of  a  type  which  is  not  uncommon  among  older  subjects,  and  must  be 
interpreted  either  as  decreased  flexibility  of  the  arteries  or  less  effective  vasomotor 
control.  It  emphasizes  the  fact  shown  by  experience  that  the  best  age  for  flying  is  the 
early  twenties — a  man  of  36  has  already  begun  to  grow  old. 

Preliminary  blood  pressures :  Reclining,  124 ;  standing,  132 ;  after  exercise,  142  ;  and 
two  minutes  later,  124. 

During  the  test  the  systolic  pressure  rises  at  the  start  and  remains  at  about  160. 
As  often  happens  when  systolic  is  high,  there  is  not  a  very  marked  rise  in  pulse.  There 
is  no  evidence  of  circulatory  fatigue,  and  he  reaches  a  low  oxygen  percentage  with 
excellent  command  of  his  faculties.  His  present  performance  is  first  class,  but  it  is 
unlikely  that  he  would  remain  in  condition  long  if  he  runs  such  a  blood  pressure  when 
he  flies.  Class  B. 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  63 

evidence  of  circulatory  fatigue  after  the  flight.  The  vasomotor  tone 
fell  in  at  least  65  per  cent  of  the  men ;  in  some  the  fall  was  slight,  but 
in  several  instances  it  exceeded  30  per  cent.  In  view  of  the  limited 
amount  of  field  study  of  the  aviator  and  the  fact  that  the  flying  has 
been  at  comparatively  low  altitudes,  final  conclusions  can  not  yet  be 
made.  From  the  data  available  it  appears  that  low  flying  fatigues 
the  circulatory  mechanism,  but  not,  however,  as  much  as  the  same 
time  spent  in  physical  work. 

THE  HEMOGLOBIN  WHEN  UNDER  A  DECREASING  OXYGEN  SUPPLY. 

Since  an  increase  in  the  percentage  of  hemoglobin  in  the  blood  is 
one  of  the  most  important  of  the  low  oxygen  compensations  found 
to  occur  in  men  and  animals  living  at  high  altitudes  on  mountains, 
it  is  interesting  to  find  that  it  may  also  occur  during  short  exposure 
to  low  oxygen.  The  rebreathing  test  of  not  more  than  30  minutes 
duration  is  too  short  a  period  of  time  to  permit  a  concentration  of 
hemoglobin  in  the  majority  of  men.  Only  an  occasional  subject  may 
show  a  definite  concentration.  In  order  to  test  out  the  part  that  the 
blood  changes  may  play  as  a  compensatory  factor  for  oxj^gen  want 
in  such  a  short  period  as  the  aviator  spends  in  the  air,  a  series  of  ex- 
periments are  now  being  made  in  the  pneumatic  or  low  pressure 
chamber  and  also  under  low  oxygen.  In  these  the  subject  is  held  at 
a  chosen  pressure  or  a  given  percentage  of  oxygen  for  from  40  to  90 
minutes,  the  entire  experiment  lasting  as  much  as  two  or  two  and  a 
half  hours.  The  hemoglobin  has  been  determined  by  two  methods, 
the  Gower-Haldane  hemoglobinometer  and  the  Du  Bousque  colorime- 
ter, on  blood  taken  from  a  finger  or  an  ear,  and  also  from  a  vein  in 
the  arm. 

At  least  25  per  cent  of  all  men  examined  have  shown  a  well-de- 
fined increase  in  the  percentage  of  hemoglobin,  and  the  majority  some 
evidence  of  concentration.  We  have  found  that  the  blood  from  the 
finger  or  ear  and  from  the  vein  showed  it  equally  well  by  the  two 
methods  used  in  the  determinations.  The  following  illustrates  the 
amount  of  concentration:  Normal  per  cent  of  hemoglobin  with  the 
Gower-Haldane  hemoglobinometer,  from  a  finger  100,  from  a  vein  90. 
After  80  minutes  under  low  oxygen,  60  of  which  were  spent  at  10  per 
cent  oxygen,  finger  105,  vein  102.  The  amount  of  concentration  has 
been  as  great  as  9.5  per  cent.  It  has  been  most  clearly  induced  at 
pressures,  and  percentages  of  oxygen,  corresponding  to  between 
18,000  and  20,000  feet.  Almost  all  of  the  men  have  had  to  be  held  at 
the  high  altitudes  20  or  more  minutes  before  concentration  began  to 
be  evident. 

Since  the  blood  changes  do  not  always  occur,  and  are  slow  in  ap- 
pearing when  they  do,  the  determination  of  hemoglobin  during  a  re- 
breathing  test  has  not  been  made  a  part  of  the  routine  examination. 


64 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


Legend 


G.,%'        »um»mn»      Pulse  K  — .  - 
i  Diast.  B.  P.  Pulse  Pressure 


.  Reap,  in  decil.  per  min.  •  • •  . .  •  -£y st.  B.  P 

Accom.  in  mm.  Convergence  in^mm. 


»    n 
.TIME 


n     0     1     2     3     4     5     6  ,7     8     8    10    11    1-2   13   14  15   16.17   18   19  20   21J22^23_JJ4  25. 2«, 27. 28^29^80  31   32   33 

IN  MINUTES 

CHABT  9. 


MANUAL  OP   MEDICAL  RESEARCH  LABORATORY. 


65 


•O.,%  •iu:i*iiui»imi>    Puise  «„___..  jResp.  in  cfecil.  per  tnin.      •  •.,.....«  SysL  B,  f 

Diast. .3.  P.  Pulse  Pressure  Accom.  in  mm.  Convergence  in  mm. 


l.'iO 


no 


TIME  -JJT-'MlXrTKS" 


No.  63. — J.  E.  S.  CADET.  Age  21  years  1  month. 

Left  hospital  three  days  ago,  where  he  was  laid  up  for  a  week  with  influenza.  Feeling 
fairly  well  to-day,  though  not  up  to  his  usual  form. 

The  first  chart  is  typical  of  a  man  out  of  condition,  rather  high  systolic  pressure, 
psychic  rise  in  both  pulse  and  pressure,  followed  by  a  sudden  faint  at  about  8  per  cent. 
In  this  the  diastolic  pressure  fell  practically  to  zero ;  the  systolic  pressure  and  pulse 
also  broke  sharply,  as  may  be  seen  by  the  slow  recovery  after  the  experiment  was 
terminated. 

He  was  tested  again  two  weeks  later  (chart  not  given),  and  made  a  very  good  run, 
with  the  exception  of  a  rather  high  blood  pressure  (148).  In  this  test  he  was  not 
completely  inefficient  when  taken  off  at  5.5  per  cent.  After  two  weeks  he  was  given  a 
third  test  (second  chart),  which  entitles  him  to  an  AA  rating.  The  systolic  pressure 
stays  below  140,  there  is  no  break  in  diastolic,  and  there  is  a  moderate,  healthy  rise 
in  pulse. 

This  case  illustrates  the  very  serious  effects  of  temporary  indisposition. 

89119—18 5 


66  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

THE    RELATIVE   VALUE   OF   THE    COMPENSATORY    FACTORS. 

In  order  that  a  better  understanding  might  be  had  of  the  inter- 
play of  the  compensatory  factors,  when  man  ascends  quickly  to  very 
high  altitudes  and  remains  only  a  short  time,  a  few  hours  at  the 
most,  a  number  of  experiments  have  been  made  with  men  in  the 
pneumatic  chamber  and  also  under  low  oxygen  in  which  they  have 
been  held  for  an  hour  or  two  under  conditions  corresponding  to 
altitudes  of  15,000  to  20,000  feet.  In  all  of  these,  two  of  the  compen- 
satory changes,  those  in  breathing  and  in  circulation,  have  appeared 
almost  simultaneously  and  increased  steadily  with  the  gradually  in- 
creasing altitude.  When  the  desired  altitude  was  reached  and  then 
maintained  the  breathing  either  continued  at  the  depth  it  had 
acquired  during  the  period  of  progressive  change  or  it  became  still 
deeper  for  a  time.  The  pulse  rale,  which  gives  an  index  of  the  in- 
crease in  the  rate  of  blood  flow,  accelerated  during  the  period  corre- 
sponding to  ascent ;  and,  then,  .when  the  altitude  was  held,  usually 
remained  constant,  or,  in  some  of  the  men,  retarded  somewhat  after 
the  hold  began.  A  slowing  of  the  pulse  rate,  when  an  altitude  was 
maintained  for  a  time,  was  so  frequently  observed  that  we  sought  for 
an  explanation  of  the  decrease  in  rate.  In  a  number  of  men  it  was 
found  that  the  heart  was  being  relieved  by  other  compensatory 
factors.  "  In  such  cases  one  or  the  other  or  both  of  two  changes 
occurred.  There  occurred  either  a  further  deepening  of  the  breath- 
ing, or  a  concentration  of  the  hemoglobin,  or  both  of  these  changes 
took  place  together.  Often  the  breathing,  after  increasing  in  amount 
during  the  ascent,  held  at  a  constant  increased  depth  during  the  stay 
at  the  given  altitude;  but  in  such  the  hemoglobin  was  found  to  be 
concentrating  as  the  pulse  rate  slowed. 

An  unusual  but  interesting  case  was  found  in  a  man  whose  breath- 
ing failed  to  respond  to  the  changes  in  altitude.  He  did  not  tolerate 
the  low  pressure  well  at  first,  but  felt  better  after  some  time  had 
been  spent  at  the  chosen  pressure.  In  this  man  the  heart  accelerated 
decidedly  and  later  his  hemoglobin  concentrated  about  8  per  cent. 
His  improvement  occurred  when  the  hemoglobin  shoAved  concen- 
tration. 

As  yet  no  attempt  has  been  made  to  study  oxygen  secretion  during 
our  rebreathing  experiments  or  in  the  pneumatic  chamber. 

Our  studies  show  that  during  short  exposures  to  high  altitudes,  or 
low  oxygen,  such  as  the  aviator  experiences,  the  compensatory  re- 
actions of  the  body  to  a  decreased  oxygen  are  made  almost  entirely 
by  the  circulation  and  by  the  breathing.  A  few  men  may,  after  the 
lapse  of  an  hour  or  more,  secure  some  benefit  from  a  slowly  develop- 
ing concentration  of  the  hemoglobin  of  the  blood.  The  order  of  re- 
sponse by  the  adaptive  mechanisms  is  not  that  of  the  good  reaction 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  67 

seen  among  mountaineers,  in  whom  the  breathing  first  responds  while 
the  other  compensatory  changes  take  place  more  slowly.  The  reaction 
resembles  more  nearly  that  seen  during  an  attack  of  mountain  sick- 
ness among  mountaineers.  In  such  men  the  heart  beat  is  greatly  ac- 
celerated during  the  attack.  The  aviator,  it  appears,  must  depend 
largely  upon  his  heart  and  his  breathing  for  compensation  to  the 
fall  in  oxygen  which  he  encounters  as  he  ascends. 

The  length  of  time  taken  to  reach  a  low  oxygen  in  the  rebreathing 
test  will  profoundly  alter  the  ability  to  endure  extremely  low  per- 
centages. If  the  oxygen  is  lowered  rapidly,  the  candidate  compen- 
sates to  a  lower  percentage  than  is  possible  where  the  rate  of  decrease 
in  the  oxygen  is  slower.  Three  rebreathing  experiments  made  on  the 
same  subject  illustrate  the  condition.  The  volume  of  air  was  so  small 
for  the  first  test  that  in  23£  minutes  the  oxygen  was  lowered  to  6.3 
per  cent,  at  which  the  subject's  power  of  compensation  failed.  The 
next  day,  rebreathing  a  larger  volume  of  air  for  38  minutes,  he  com- 
pensated to  7  per  cent  only.  On  the  following  day,  in  a  test  of  85 
minutes'  duration,  compensation  failed  at  8.7  per  cent  of  oxygen. 
Individual  differences  will  be  found;  in  some  men  time  has  a  more 
profound  influence  than  in  others.  Thus,  another  subject  compen- 
sated in  a  test  of  36  minutes  down  to  7.5  per  cent  and  in  one  of  90 
minutes  to  8  per  cent  of  oxygen.  Therefore,  when  testing  ability  to 
endure  low  oxygen,  some  allowance  must  be  made  for  the  time  taken 
to  reach  a  given  percentage.  If  each  of  two  men  tolerate  down  to  7 
per  cent  oxygen  but  one  is  carried  down  in  20  and  the  other  in  40 
minutes,  the  one  who  endures  for  40  minutes  will  have  the  better 
power  of  compensation. 

Control  tests  have  been  conducted  in  the  pneumatic  or  low-pressure 
chamber  to  determine  the  reliability  of  the  rebreathing  test.  A  sub- 
ject was  first  under  observation  in  a  rebreathing  test,  and  on  the  fol- 
lowing day  taken  into  the  low-pressure  chamber  for  similar  observa- 
tions, while  the  pressure  was  lowered  at  the  same  rate  that  the  oxygen 
had  been  absorbed  in  the  rebreathing  test.  The  breathing,  pulse  rate, 
and  blood  pressures  reacted  about  the  same  in  each  experiment.  In 
order  that  a  comparison  might  be  made  of  the  breathing  under  the 
two  conditions  the  alveolar  air  was  analyzed  from  time  to  time  dur- 
ing .each  kind  of  test.  A  fall  in  the  alveolar  carbon  dioxide  and 
oxygen  pressure  occurred  in  both  experiences.  The  average  amount 
of  fall  for  eight  men  at  the  per  cent  of  oxygen  or  pressure  corre- 
sponding to  20,000  feet  was  for  carbon  dioxide  during  rebreathing 
8.5  millimeters  and  low  pressure  9.3  millimeters;  for  the  oxygen  in 
rebreathing  66.2  millimeters  and  low  pressure  68.8  millimeters. 
These  figures  show  that  the  increase  in  the  breathing  and  lung  venti- 
lation was  about  the  same  under  the  two  different  low-oxygen  experi- 
ences. The  pulse  rate  also  was  found  to  begin  to  accelerate  at  about 


68  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

the  same  time  in  each  kind  of  test  and  to  accelerate  in  equal  degree. 
Those  and  other  physiological  observations  made  on  men  undergoing 
the  rebreathing  test  or  under  decreasing  atmospheric  pressure  prove 
that  the  same  compensations  are  used  by  the  body  in  each,  and  those 
we  know  are  the  adjustments  made  to  the  influence  of  oxygen  want. 

ALVEOLAR  AIR  PRESSURES  IN  THE  LOW  PRESSURE   CHAMBER  AND   ON   THE 
REBREATHING  APPARATUS. 

Whether  the  individual  is  in  the  low-pressure  chamber  or  on  the 
rebreathing  apparatus  he  can  equally  well  be  subjected  to  gradually 
decreasing  oxygen  pressure.  The  rebreathing  machine  has  been 
shown  to  be  equivalent  to  the  low-pressure  chamber  for  testing  the 
ability  of  an  individual  to  adapt  himself  to  low  oxygen  pressure  so 
far  as  circulatory  and  psychological  reactions  are  concerned.  A  con- 
sideration of  the  respiratory  factors  in  each  was  necessary  in  order  to 
complete  the  comparison.  The  respiratory  factors  to  be  considered 
are:  First,  the  alveolar  air  pressures;  second,  the  volume  per  minute 
and  rate ;  third,  the  blood  gases. 

A  series  of  experiments  were  carried  out  to  show  the  changes  in  the 
alveolar  air  pressures  during  an  ordinary  rebreathing  test  lasting 
about  30  minutes,  in  which  the  subject  was  exposed  to  a  fall  of  oxygen 
per  cent  from  20.96  to  9.8,  or  corresponding  barometric  pressures  of 
760  mm.  to  350  mm.  (20,000  feet).  The  subject  was  put  on  the  re- 
breather  and  samples  of  the  alveolar  air  were  taken  every  4  or  5 
minutes  until  the  end  of  the  run.  The  time  and  the  oxygen  per  cent 
of  the  rebreathed  air  were  noted  and  the  corresponding  barometric- 
pressure  for  each  oxygen  per  cent  determined.  The  same  subject  was 
taken  into  the  low-pressure  chamber  a  few  days  later  and  the  baro- 
metric pressure  was  lowered  according  to  the  rebreathing  schedule 
previously  made.  Alveolar  air  samples  were  taken  at  corresponding 
minutes  and  altitudes.  Both  series  of  alveolar  air  samples  were 
analyzed  with  the  Henderson-Orsat  gas  analyzer  and  the  partial 
pressure  calculated  allowing  40  mm.  Hg.  for  the  tension  of  water 
vapor.  The  curves  of  each  subject  were  plotted  on  the  same  chart. 

The  curves  of  the  alveolar  air  pressures  plotted  (see  chart  9A)  from 
the  data  obtained  in  the  low-pressure  chamber  and  with  the  re- 
breathing  apparatus  are  striking  in  their  similarity.  In  many  cases 
they  practically  coincide.  The  oxygen  tension  in  the  alveolar  air  of 
eight  subjects  on  the  rebreathing  machine  fell  from  102.5  mm.  Hg. 
to  36.3  mm.  during  runs  from  760  mm.  to  350  mm.,  or  20.96  per  cent 
oxygen  to  9.8  per  cent.  This  is  an  average  fall  of  62.2  mm.  for  20,000 
feet  (see  Table  1).  In  10  corresponding  experiments  in  the  low- 
pressure  chamber  the  alveolar  oxygen  tension  fell  from  104.6  mm.  to 
35.8  mm.  during  the  ascent  to  20,000  feet.  The  average  fall  was 
68.8mm.  (see  Table  2). 


,Resp.  in  decil.  per  min.  , 4Syst.  B.  P 


B 


--r— i 1 1 1 1— j j 1 

•V.B.R.      Age   23-2/12 

Mitral  insufficiency  and  Btenoeis.        — \ — r 
High  Mood -pre?  sure,  labored  res- 
piration.  Early  inefficiency. 
"Clans  D" 


i  / 

r-f-l--h-H-t-! 
j/l- 

_l4lpilpp — 

-i-[-^--^-H 


1 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


69 


In  the  previous  eight  cases,  in  which  the  alveolar  oxygen  pressure 
was  determined  on  the  rebreathing  apparatus,  the  alveolar  carbon 
dioxide  pressure  fell  from  42.6  mm.  to  34.1  mm.,  an  average  fall  of 
8.5  mm.  (see  Table  3).  In  the  10  corresponding  cases  in  the  low- 


CHABT  9A. 

pressure  chamber  the  alveolar  carbon  dioxide  tension  fell  from  40.1 
to  30.8  mm.,  an  average  fall  of  9.3  mm  (see  Table  4). 

The  curve  of  the  alveolar  oxygen  tension  obtained  in  the  low- 
pressure  chamber  or  on  the  rebreather  is  essentially  a  straight  line. 
That  of  the  alveolar  carbon  dioxide  tension  is  not  so  regular.  Certain 
irregularities  in  the  curve  were  found  which  could  be  correlated  with 
changes  in  lung  ventilation  as  indicated  by  the  volume  of  air  breathed 


70 


MANUAL  OF   MEDICAL  RESEARCH  LABORATORY. 


per  minute.  In  seven  cases  there  was  a  gradual  fall  of  alveolar  carbon 
dioxide  pressure  as  the  barometric  pressure  was  lowered  from  760  mm. 
to  350  mm.  (20,000  feet).  In  two  cases  it  remained  nearly  constant 
until  about  550  mm.  and  then  fell  fairly  rapidly. 

An  examination  of  tables  1,  2,  3,  4,  and  of  the  plotted  curves  shows 
very  definitely  that  the  changes  of  the  alveolar  air  pressure  during 
exposure  to  progressively  diminished  oxygen  pressure  are  quite  simi- 
lar and  that  the  respiratory  factors  as  well  as  the  circulatory  and 
psychological  reactions  are  the  same  in  the  two  methods. 
TABLE  1. — Rebreathing  O2. 


Subject. 


760  mm.       350  mm. 


Griest 106.5  39.9 

Browning 106.0  33.8 

Pierce 103.0  39.0 

Burlingame 109. 0  38. 0 

Jenkins 97. 5  24. 0 

Smart 99.0  38.0 

Kuempel 97.5  36.0 

McKinnie 101. 2  42. 0 

Average 102.5  36.3=66.2 

Average  O5  tension,  760  mm 102. 5  mm. 

Average  O2  tension,  350  mm 36. 3  mm. 

Average  fall  for  20,000  feet  rise 66. 2  mm . 

TABLE  2. — Low  pressure  Oa. 

Subject.  760  mm.  350  mm. 

Neuswanger 116. 7  33. 4 

McKinnie 104.2  38.0 

Dorsey 94.5  34.4 

Smart 92.0  36.0 

Merrill 104.5  43.0 

Kuempel 105.5  31.2 

Jenkins 108. 0  34. 4 

Burlingame 106. 2  33. 4 

Leinbach 106.2  36.1 

Pierce 108.7  38.7 

Average 104.6  35.8-68.8 

Average  Oa  tension,  760  mm, 104. 6  mm. 

Average  Os  tension,  350  mm 35. 8  mm. 

Average  fall  for  20,000  feet  rise 68. 8  mm. 

TABLE  3. — Relreathing  CO2. 

Subject.  760  mm.  350  mm. 

Burlingame 43. 5  39. 9 

Browning 40. 9  35. 4 

Greist 42.4  39.3 

Pierce 43.1  32.6 

Jenkins 45.6  18.0 

Kuempel 43.8  34.8 

McKinnie 39.2  33.0 

Smart 42.5  39.8 

Average 42.6  34.1—  8.5 

Average  COj  tension,  760  mm 42. 6  mm. 

Average  COj  tension,  350  mm 34.1  mm. 

Average  fall  for  20,000  feet  rise .* 8.5mm. 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


71 


TABLE  4. — Low  pressure  CO2. 


Subject. 

760mm. 

350mm. 

Smart  

39.8 

37.2 

Burlingame  

41.2 

34.7 

Pierce      .             

39.0 

30  4 

Jenkins  

38.7 

27.3 

Kuempel  

39.8 

24.4 

McKinnie  

40.4 

31.6 

Leinbach       ..             .         .          

37.8 

27.6 

Merrill  

40.0 

29.7 

Dorsey  

44.4 

30.8 

Neuswanger  

40.4 

34.7 

A  verage  

40.1 

30.8-  9.3 

Average  CO2  tension,  760  mm 40. 1  mm. 

Average  CO3  tension,  350  mm 30. 8  mm. 

A  verage  fall  for  20,000  feet  rise 9. 3  mm. 

From  these  preliminary  experiments  we  should  infer  that  in  the 
ordinary  short  experiments  in  which  the  barometric  pressure  is 
lowered  to  about  350  mm.  in  20  minutes,  similar  to  the  conditions 
during  a  rebreathing  test,  the  alveolar  carbon  dioxide  pressure  starts 
to  fall  with  the  barometer.  The  law  of  Haldane  and  Preistly,  which 
states  that  during  rest  under  ordinary  conditions  the  alveolar  carbon 
dioxide  pressure  remains  constant,  holds  good  only  when  the  baro- 
metric pressure  remains  constant  also.  These  experiments  point  to 
the  view  that  the  alveolar  carbon  dioxide  pressure  does  not  remain 
constant  under  progressively  diminished  barometric  pressure  to  the 
extent  formerly  believed. 

A  few  men  were  taken  to  15,000  feet  at  the  rate  of  1,000  feet  per 
minute,  held  there  for  five  minutes  and  then  dropped  at  the  same 
rate  to  2,000  feet.  This  procedure  was  repeated  three  times  in  suc- 
cession. The  alveolar  gas  pressures  were  remarkably  constant  for 
the  same  altitude  in  each  of  these  cases.  Table  5  gives  the  result 
in  two  such  cases. 

TABLE  5. 


Barometer. 

760  mm. 

425  mm. 

700mm. 

425mm. 

700mm. 

425  mm. 

760  mm. 

1    /Oj... 

104 

40 

91 

40 

92 

39 

98 

\Cos                            

41 

39 

43 

39 

41 

39 

42 

o     /O  ».. 

106 

51 

96 

47 

95 

48 

95 

a  \cos  

41 

29 

34 

32 

36 

30 

41 

In  a  number  of  experiments  the  subjects  were  exposed  to  low  oxy- 
gen tension  for  longer  periods.  When  the  individual  is  held  for  an 
hour  or  more  at  a  low  barometric  pressure,  380  mm.  for  example 
(18,000  feet),  the  alveolar  air  pressures  tend  to  remain  remarkably 
constant.  In  10  cases  the  average  alveolar  carbon  dioxide  pressure 
at  the  end  of  96  minutes  was  only  about  1  mm.  lower  than  when  the 
low  barometric  pressure  was  first  reached.  The  fact  that  there  was 
no  striking  change  in  alveolar  carbon  dioxide  pressure  during  pro- 
longed exposure  to  a  given  low  barometric  pressure  led  us  to  examine 
the  volume  of  air  breathed  per  minute  during  these  exposures  and 
the  carbon  dioxide  capacity  of  the  blood  at  the  beginning  and  at 
the  end. 


72  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

Eight  experiments  were  carried  out  to  determine  the  volume  of  air 
breathed  per  minute.  The  subject  wore  an  American  Tissot  mask  and 
inspired  through  a  gas  meter.  The  resistance  of  the  meter  was  not 
great  enough  to  cause  any  change  in  the  rate  or  volume  of  respiration, 
as  shown  by  control  runs  for  periods  of  one  to  two  hours.  The  average 
volume  breathed  per  minute  at  760  mm.  was  7  liters.  With  the  ascent 
to  380  mm.  an  increase  in  ventilation  took  place,  attaining  its  maxi- 
mum about  10  minutes  after  the  low  barometric  pressure  had  been 
reached.  In  six  cases  of  these  eight  the  lung  ventilation  decreased 
more  than  a  liter  while  the  low  barometric  pressure  was  being  held. 
In  several  cases  the  breathing  decreased  to  its  original  volume  before 
the  ascent.  During  these  exposures  the  type  of  breathing  frequently 
changed  from  shallow  rapid  to  slow  and  deep  respiration.  In  one 
case  the  rate  fell  from  14  per  minute  to  9  within  20  minutes  after 
reaching  380  mm. 

During  short  exposures  to  progressively  diminishing  oxygen  pres- 
sure with  either  the  rebreather  or  in  the  low-pressure  chamber  the 
lung  ventilation  increases.  In  the  rebre; idling  experiments  the  first 
respiratory  response  has  been  found  to  be  between  16  and  14  per  cent 
of  oxygen.  In  the  low-pressure  chamber  in  a  few  experiments  the 
response  in  breathing  occurred  at  about  8,000  feet,  or  at  approximately 
15  per  cent  of  oxygen.  In  several  instances,  however,  the  response 
began  immediately. 

CARBON  DIOXIDE  CAPACITY  OF  THE  BLOOD. 

Both  on  the  rebreathing  apparatus  and  in  the  low-pressure  cham- 
ber the  carbon  dioxide  capacity  of  the  blood  was  determined  before 
the  experiment  and  at  the  end,  while  the  subject  was  still  under  the 
influence  of  low  oxygen.  On  the  rebreathing  apparatus  12  cases  were 
examined,  some  of  which  reached  6.2  per  cent  of  oxygen  and  showed  a 
marked  respiratory  reaction.  There  was,  however,  no  noticeable  low- 
ering of  the  carbon  dioxide  capacity  of  the  whole  blood  as  determined 
by  the  Henderson  method.  Even  in  the  low-pressure  chamber,  where 
the  subject  was  exposed  to  a  pressure  of  380  mm.  for  periods  of  over 
an  hour,  no  decreased  alkalinity  of  the  blood  could  be  detected.  This 
is  not  surprising  in  view  of  the  fact  that  the  volume  per  minute 
breathed  was  lowered  at  the  end  of  these  experiments. 

HEMOGLOBIN    CHANGES. 

One  of  the  factors  which  compensate  for  prolonged  exposure  to  low 
atmospheric  pressure  has  been  shown  to  be  the  hemoglobin.  On 
Pike's  Peak  a  relative  increase  in  the  per  cent  of  hemoglobin  takes 
place,  which  is  later  superseded  by  an  actual  increase  in  the  number 
of  red  cells.  The  ordinary  rebreathing  test  is  too  short  to  permit  of 
a  concentration  of  hemoglobin,  but  in  experiments  in  the  low-pres- 
sure chamber,  where  the  subject  is  held  for  periods  of  an  hour  or  two, 


MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 


73 


a  well-defined  increase  has  been  found  with  the  Gower-Haldane 
hemoglobinometer  in  blood  taken  from  the  finger  and  from  the  vein 
in  more  than  25  per  cent  of  the  cases  examined.  In  several  cases  the 
amount  of  increase  was  more  than  6  per  cent  and  in  one  case  as  high 
as  9  per  cent.  In  a  few  instances  the  number  of  erythrocytes  .was 
determined  and  an  increase  found,  which  in  one  case  was  9.6  per  cent 
and  in  another  case  14  per  cent. 

CHANGES  IN  PULSE  RATE  DURING  EXPOSURE  TO  LOW  OXYGEN  PRESSURE. 

In  a  series  of  experiments  in  the  low-pressure  chamber,  in  which 
the  barometric  pressure  was  lowered  to  380  mm.  (18,000  feet)  at  the 
rate  of  1,000  feet  per  minute  and  held  at  that  altitude  for  periods 
varying  from  60  to  104  minutes,  the  pulse  rate  was  taken  every  minute 
during  the  procedure.  The  curve  of  the  pulse  changes  plotted  against 
the  variation  in  the  barometer,  and  time  shows  that  the  rate  increases 
as  the  barometric  pressure  decreases,  but  does  not  maintain  its  maxi- 
mum during  the  hold  at  the  high  altitude. 

In  18  cases  out  of  20  there  was  a  slowing  of  the  pulse  rate  while 
the  low  pressure  was  being  maintained.  The  average  pulse  rate  at 
760  mm.  was  73  per  minute.  During  the  ascent  to  380  mm.  the 
average  increase  in  the  pulse  rate  was  19  beats,  or  about  1  beat  per 
1 ,000  feet.  This  increase  in  the  pulse  rate  began  between  2,000  and 
3,000  feet  in  an  average  of  34  cases.  In  only  4  cases  did  it  appear 
as  late  as  8,000  feet.  In  no  other  case  was  it  above  4,000  feet. 

The  maximum  pulse  rate  was  reached  in  24  minutes  after  the  be- 
ginning of  the  ascent,  or  6  minutes  after  the  barometric  pressure  of 
380  mm.  have  been  attained.  During  the  hold  of  this  altitude,  aver- 
aging 86  minutes,  the  average  pulse  slowed  to  84  beats  per  minute,  an 
average  drop  of  8  beats.  The  individual  decrease  in  pulse  rate 
varied  from  5  to  14  beats  and  in  7  of  the  20  cases  it  was  10  beats  or 
more.  (See  Table  6.) 

TABLE  6. — Change  in  pulse  rate  during  exposure  to  low  oxygen  tension. 


Experiment. 

Normal. 

Maxi- 
mum. 

Time 
reached. 

Maxi- 
mum. 

Time 
reached. 

Fall. 

Total 
time. 

1       

64 

91 

23 

81 

62 

10 

81 

2       

70 

94 

31 

86 

76 

8 

82 

3  

65 

102 

26 

102 

49 

1 

64 

4        

88 

99 

25 

93 

81 

6 

104 

5      

75 

89 

30 

83 

72 

6 

86 

6    

72 

87 

22 

82 

82 

5 

92 

7        

71 

86 

20 

78 

75 

8 

91 

8       

73 

93 

22 

81 

75 

12 

77 

9     

78 

94 

22 

80 

35 

14 

61 

10         

74 

120 

24 

106 

56 

14 

68 

11       

69 

87 

27 

78 

85 

9 

96 

12   

80 

100 

22 

'  90 

54 

10 

65 

13        

59 

80 

22 

70 

72 

10 

78 

14  

60 

82 

24 

74 

77 

8 

79 

15           

81 

88 

22 

82 

64 

6 

78 

16        

95 

99 

25 

99 

80 

85 

17               

67 

90 

28 

84 

72 

6 

78 

18           

76 

88 

26 

81 

'  81 

7 

100 

19    

72 

94 

24 

89 

68 

5 

71 

20  

76 

82 

22 

71 

68 

11 

91 

Average  

73.25* 

91.80 

24.35 

84.0 

69.2 

7.8 

85.75 

74  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

THE  RELATIVE  VALUE  OF  THE  COMPENSATORY  FACTORS. 

The  factors  which  are  involved  in  the  compensation  during  very 
long  exposures  to  low-oxygen  pressures,  as  on  Pike's  Peak,  have  been 
shown  to  be,  first,  the  circulation,  as  indicated  by  the  pulse  rate  and 
the  'blood  pressure  ;  second,  the  respiration,  as  shown  by  the  rate, 
volume  per  minute,  carbon  dioxide  and  oxygen  pressures  in  the  alve- 
olar air,  and  the  carbon  dioxide  capacity  of  the  blood;  third,  the 
hemoglobin;  fourth,  secretion  of  oxygen  by  the  lung  epithelium. 
Evidence  bearing  on  the  nature  of  the  first  three  factors  has  been 
secured  in  these  experiments.  There  is  undoubtedly  a  considerable 
amount  of  coordination  and  interplay  of  the  various  factors.  In 
the  rebreathing  tests  the  circulation  responds  first,  later  the  respira- 
tion. In  these  tests  the  subject  is  pushed  until  he  shows  signs  of  fail- 
ing in  compensation.  The  situation  is  different  when  the  individual 
is  kept  at  a  given  low  pressure  in  the  pneumatic  chamber.  Both  the 
pulse  and  the  respiration  accelerate  during  the  ascent,  but  in  a  great 
many  cases  the  pulse  rate  falls  while  the  chosen  pressure  is  being 
maintained.  We  should  look  for  compensation  by  other  factors  in 
these  cases,  either  by  means  of  increased  lung  ventilation,  concentra- 
tion of  hemoglobin,  or  possibly  secretion  of  oxygen  through  the 
lung  epithelium.  In  a  number  of  men  the  heart  was  relieved  by  fur- 
ther deepening  of  the  breathing  or  a  concentration  of  the  hemo- 
globin, or  both  changes  occurred.  A  number  of  cases  have  been  ob- 
served in  which  a  concentration  of  hemoglobin  took  place  while  the 
heart  rate  slowed  (see  chart  !OA),  and  the  lung  ventilation  either 
maintained  its  own  or  became  less. 

An  unusual  but  interesting  case  was  found  in  a  man  whose  breath- 
ing failed  to  respond  to  the  change  in  altitude.  He  did  not  tolerate 
the  low  pressure  well  at  first,  but  later  his  condition  improved  while 
the  given  low  pressure  was  being  maintained.  The  heart  rate  accel- 
erated markedly  and  later  his  hemoglobin  concentrated  above  8 
per  cent.  His  improvement  occurred  when  his  heart  was  relieved  by 
the  concentration  in  hemoglobin. 

Our  studies  show  that  during  short  exposures  to  high  altitudes  or 
low  oxygen,  such  as  the  aviator  experiences,  the  compensatory  re- 
actions of  the  body  are  made  almost  entirely  by  the  circulation  and 
the  breathing.  Some  men  may  secure  some  benefit  after  an  hour  or 
more  from  a  slowly  developing  concentration  of  the  hemoglobin  of 
the  blood.  The_order  _of  response  by.  the  adaptive  mechanisms  is  not 

among  mountaineers,  in  whom  the 


breathing  first  responds  while  the.  otEer^^omjpensatory  changes  more 
slowrly  occur.  The  reaction  resembles  more  nearly  that  seen  during 
an  attack  of  mountain  sickness  among  mountaineers.  In  such  men 


MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 


75 


the  heart  beat  is  greatly  accelerated  during  the  attack.  The  aviator 
must  depend  largely  on  his  heart  and  his  breathing  for  compensation 
to  the  fall  in  oxygen  pressure  which  he  encounters  during  an  ascent. 

III.— THE  EFFECTS   OF   LOW  ATMOSPHERIC   PRESSURE  ON   THE 
CIRCULATORY  SYSTEM. 

It  has  long  been  recognized  in  an  unscientific  way  that  high  alti- 
tudes are  "bad  for  a  weak  heart."  At  such  elevations  as  those  of 
Denver,  Phoenix,  or  Mexico  City,  patients  with  any  degree  of  cardiac 
incompetence  noticed  undue  shortness  of  breath,  palpitation,  general 
weakness,  and  occasionally  there  have  been  cases  of  sudden  decom- 
pensation and  acute  pulmonary  congestion.  Even  much  lower  eleva- 


CHABT  10A. 

tions  have  been  suspected  by  the  laity  of  causing  distinct  heart  symp- 
toms. The  reason  for  this  has  not  been  understood,  because  very 
little  research  work  from  this  point  of  view  has  been  carried  on.  The 
physiological  results  on  Monte  Rosa,  Pike's  Peak,  etc.,  have  had  as 
participants  and  subjects  almost  entirely  healthy  men  of  the  moun- 
taineering type,  and  in  these  there  has  been  so  little  evidence  of  cir- 
culatory strain,  to  say  nothing  of  actual  incompetence,  that  it  was 
generally  assumed  that  the  supposed  dangers  from  the  heart  were 
mythical  or  at  least  much  exaggerated. 

As  a  part  of  the  research  now  being  carried  on  at  the  Medical 
Research  Laboratory  of  the  Air  Service  at  Mineola  the  behavior  of 


76  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

the  heart  and  circulation  has  received  much  attention.  We  have 
had  almost  ideal  conditions  for  this  study,  having  at  our  disposal 
two  methods  of  producing  physiological  effects  comparable  to  those 
of  aviation.  In  these  effects  the  determining  factor  is,  of  course,  low- 
oxygen  tension  in  the  air. 

In  the  rebreathing  apparatus  the  percentage  of  oxygen  is  grad- 
ually lowered,  while  in  the  low-pressure  chamber  the  percentage 
remains  the  same,  but  the  barometric  pressure  may  be  reduced  to 
any  desired  point.  In  either  case  accurate  observations  of  heart  and 
circulation  are  conveniently  made.  The  two  methods  give  strictly 
parallel  results,  which  tally  very  accurately  with  actual  conditions 
in  the  air  as  far  as  it  has  been  possible  to  investigate  the  latter 
directly  or  to  judge  from  what  is  told  by  aviators  of  their  own 
experience.  The  material  studied  has  consisted  largely  of  healthy 
and  youthful  individuals,  though  even  among  supposedly  normal 
men  not  a  few  pathological  hearts  have  been  discovered,  and  from 
the  neighboring  post  hospitals  we  have  obtained  a  few  subjects  who 
were  known  to  have  definitely  abnormal  hearts.  In  the  near  future 
we  hope  to  extend  very  considerably  our  observations  on  the  grosser 
forms  of  valvular  and  myocardial  disease  and  on  cases  with  various 
degrees  of  decompensation. 

The  results  have  been  exceedingly  interesting  and  important  and 
have  so  fitted  in  with  the  experiences  and  the  problems  of  aviators 
that  they  can  not  but  be  of  the  greatest  practical  value.  They  have 
shown  that  the  ability  to  exist  at  altitudes  higher  than  the  normal 
depends  to  a  very  marked  degree  on  the  competence  of  the  circula- 
tory apparatus.  The  demand  on  the  latter  is  so  great  that  even 
slight  abnormalities  in  heart  or  blood  vessels  result  at  moderate 
heights  in  clear  signs  of  cardiac  insufficiency  and  distress.  So 
searching  indeed  is  this  test  for  cardiac  disease  of  any  kind  that  we 
have  come  to  regard  the  rebreathing  apparatus  and  the  low-pressure 
chamber  as  the  one  sure  way  of  making  a  positive  diagnosis  in  cases 
where  there  is  doubt,  and  believe  that  they  may  later  prove  to  be  of 
great  value  for  routine  clinical  work. 

At  the  same  time  the  effects  upon  the  normal  heart  have  been 
equally  striking  and  more  unexpected.  While  the  hardiest  type  of 
subject  shows  almost  no  demonstrable  effect  on  the  circulation,  others 
are  evidently  laboring  under  heavy  strain,  and  it  appears  that  dilata- 
tion of  the  heart  followed  by  collapse  is  an  extremely  common  oc- 
currence even  at  moderate  altitudes.  This  accords  with  the  known 
frequency  of  aviators  fainting  in  the  air,  almost  always  with  fatal 
results,  of  course.  We  have  been  able  to  throw  much  light  on  the 
reasons  for  this  disastrous  occurrence,  and  to  show  not  only  that  evi- 
dent disturbances  of  heart  function,  such  as  cardiac  lesions,  are  predis- 
posing causes,  but  that  temporary  indispositions  which  are  too  fre- 


MANUAL  OF  MEDICAL  RESEARCH  LABORATORY.  77 

quently  considered  trivial  have  a  very  marked  influence.  For  exam- 
ple, a  recent  infection,  a  bad  cold,  nervous  factors,  etc.,  may  so  im- 
pair a  man's  resistance  thathisTieart  will  give  out  and  he  will  faint 
during  the  test.  We  believe  that  this  has  actually  occurred  in 
numerous  cases  during  actual  flight. 

It  has  been  estimated  in  the  British  Service  that  of  all  fliers  lost  to 
active  flying  service  less  than  2  per  cent  are  put  out  by  German  bullets, 
only  8  per  cent  as  the  result  of  a  defect  in  the  plane,  the  remaining  90 
per  cent  because  of  the  physical  condition  of  the  pilot.  Our  work 
leads  us  to  believe  that  a  considerable  proportion  of  the  physical 
defects  leading  to  accident  are  the  immediate  or  late  effects  /of  strain 
on  the  circulation  under  the  influence  of  low  oxygen  tension  in 
the  air. 

PHYSIOLOGY  OF   CIRCULATION. 

The  purpose  of  the  heart  and  blood  vessels  is  to  transport  oxygen 
and  f oodjja  the  tissues  and  to  remove  ^heir  waste.  The  work  of  the 
circulatory  system  must  be  governed  by  the  changing  needs  of  the 
tissues  in  these  respects.  If  a  given  group  of  muscles,  for  example, 
are  doing  more  than  their  usual  work  they  must  have  an  increase  of 
blood  supply.  This  regulation  comes  mainly  from  the  vital  centers 
in  the  medulla,  and  consists  for  the  most  part  in  variations  in  the 
size  of  blood  vessels  (vasomotor  tone),  in  the  rate  of  the  heart,  and 
in  the  amount  of  lung  ventilation.  The  medullary  centers  are  in 
turn  activated  by  certain  chemical  factors  in  the  blood,  and  probably 
also  more  directly  by  their  own  metabolism  and  need  for  oxygen. 

The  work  done  by  the  heart  is  very  large  even  when  the  body  is  at 
rest.  It  Eas  been  calculated  that  this  amounts  in  ordinary  conditions 
to  the  work  involved  in  lifting  20  kilogram  one  meter  each  minute 
or  about  140  pounds  1  .foot.  During  exercise  this  work  is,  of  course, 
much  incmTs"ecL 

Apart  from  the  strain  thrown  upon  the  heart  by  extraordinary 
demands  it  is  evident  that  even  its  ordinary  work  requires  the  best 
of  conditions  to  be  carried  successfully.  Heart  failure  may  be  the 
result,  therefore,  not  only  of  extra  work  asked  of  the  heart,  but  of 
any  condition  which  interferes  with  its  success  in  doing  its  ordinary 
work. 

The  efficiency  of  the  heart  depends,  first,  on  the  quality  of  the 
heart  muscle;  second,  on  an  abundant  coronary  circulation,  capable 
not  only  of  supplying  ordinary  needs,  but  of  meeting  the  demand  for 
considerable  increase;  third,  on  the  quality  of  the  blood  which 
nourishes  the  heart  muscle,  especially  its  content  in  oxygen;  and 
fourth,  on  an  economical  regulation  of  the  work  of  the  heart  and  of  all 
of  the  elements  in  circulation  and  respiration,  so  that  these  functions 
may  be  carried  out  successfully,  but  without  unnecessary  strain.  The 


78  MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 

last  factor  depends  partly  on  the  accuracy  and  economy  with  which 
the  need  for  blood  flow  to  each  part  of  the  body  is  met,  and  partly  to 
the  regulation  of  general  vascular  tone,  so  that  the  blood  flow  can 
take  place  to  the  maximum  of  efficiency  without  undue  resistance 
(increased  blood  pressure). 

EFFECT  OF  LOW  OXYGEN  TENSION  ON  CIRCULATORY  PHYSIOLOGY. 

The  behavior  of  the  organism  under  low  pressure  illustrates  two 
physiological  principles : 

First,  that  the  animal  body  being  very  accurately  fitted  for  one  set 
of  environmental  conditions,  finds  itself  in  an  abnormal  situation 
if  these  conditions  are  changed  ever  so  slightly.  We  know  that  the 
body  feels  the  change  in  its  oxygen  supply  within  the  first  few 
thousand  feet,  perhaps  even  the  first  few  hundred  feet  after  ascent 
begins  from  the  surface  of  the  earth.  In  consequence  of  this  certain 
readjustments  and  compensations  are  necessary  to  'keep  the  oxygen 
tension  in  the  air. 

The  second  principle  is  that  however  accurately  the  body  is  ad- 
justed to  its  usual  surroundings,  its  powers  of  accommodation  to  new 
conditions  are  very  great,  even  when  those  conditions  represent  some- 
thing quite  out  of  the  ordinary  experience  of  the  body.  Thus  when 
adjustments  are  demanded  to  make  good  oxygen  deficiency  in  the 
atmosphere,  such  adjustments  almost  infallibly  will  be  made  and  in 
sufficient  abundance  to  keep  bodily  functions  normal  until  the  change 
from  usual  conditions  has  become  so  great  that  the  powers  of  com- 
pensation are  exhausted. 

In  other  words,  the  aviator  making  an  ascent  to  great  heights  gives 
the  picture  not  of  a  man  suffering  more  and  more  severely  from  the 
noxious  effects  of  low  oxygen  but  of  a  man  who  by  exercising  his 
powers  of  compensation  is  keeping  his  functions  normal  just  as  long 
as  these  powers  remain  equal  to  their  task. 

It  was  in  fact  a  good  deal  of  a  surprise  to  us  to  find  this  unex- 
pected normality  of  our  subjects  in  the  early  experiments,  for  not 
only  were  the  physical  and  psychic  powers  being  kept  intact  until 
an  extreme  degree  of  oxygen  want  was  reached,  but  the  adjustment 
was  so  smoothly  and  economically  made  that  our  examination  of 
heart  and  blood  vessels  and  the  respiratory  phenomena  would  have 
led  us  to  suppose  that  nothing  out  of  the  ordinary  was  going  on  at  all. 

This  statement  applies,  however,  only  to  what  we  may  refer  to  as 
the  "optimum"  type  of  subject,  and  it  was  only  by  observing  the 
behavior  of  less  ,good  subjects  that  we  arrived  at  an  understanding 
not  only  of  the  nature  of  the  compensation  which  was  making  this 
normality  possible,  but  of  the  very  great  strain  which  is  often  in- 
volved in  maintaining  it.  For  while  our  optimum  subjects  remained 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  79 

in  good  condition  and  efficient  to  very  great  heights  and  at  the  same 
time  exhibited  no  signs  of  strain  in  the  circulatory  reactions  other 
subjects  either  failed  to  make  the  compensation  and  so  became  in- 
efficient at  low  altitudes  or  made  the  compensation  only  at  the  cost 
of  very  evident  strain,  such  as  led  in  many  cases  to  cardiac  dilatation, 
circulatory  collapse,  and  fainting. 

COMPENSATION  FOR  OXYGEN  DEFICIENCY. 

I 

We  must  first  discuss  the  nature  of  the  compensating  process  and 
later  consider  how  dift'erent  types  of  organisms  respond  to  this 
demand. 

When  the  tissues  feel  a  deficiency  in  the  oxygen  supply,  demand 
is  immediately  registered  for  more.  Just  how  this  deficiency  is  felt 
and  what  the  nature  of  the  demand  is  we  need  not  discuss  at  this 
point.  (As  a  matter  of  fact,  we  have  very  little  knowledge  on  the 
subject.)  It  is  sufficient  that  such  demand  is  made  and  that  it  is 
promptly  complied  with. 

When  there  is  deficiency  in  the  oxygen  carried  by  the  blood  there 
are  two  obvious  methods  of  remedy  open — either  (a)  more  oxygen 
must  be  carried  by  the  same  amount  of  blood  or  (&)  more  blood 
must  flow  to  the  tissues  carrying  less  oxygen  per  unit  but  in  sum 
bringing  the  required  amount. 

'  j)       INCREASED  RESPIRATION. 

To  meet  the  demand  of  (#),  if  the  blood  carries  less  oxygen  per 
unit  because  of  lowered  tension  in  the  alveolar  air,  this  tension  may 
be  raised  by  increased  ventilation  of  the  lungs.  Normally  the  per- 
centage of  oxygen  in  the  alveolar  air  (that  which  comes  in  contact 
with  the  blood)  is  from  13  to  15  per  cent,  giving  a  tension  of  100 
or  more  mm.  Hg.  Increased  respiration  will  raise  this  percentage 
to  17,  18,  or  even  19.  thus  increasing  the  oxygen  tension  in  the  blood 
tola  like  degree.  In  fact,  we  know  that  increase  in  respiration  begins 
to  occur  almost  as  soon  as  the  sea-level  pressure  is  left  behind. 

The  limit  of  compensatory  mechanism  is  soon  reached  however. 
Since  the  atmosphere  contains  only  21  per  cent  oxygen,  the  alveolar 
air  can  only  with  difficulty  be  brought  up  to  19  per  cent,  and  an 
increase  from  15  to  19  per  cent  will  certainly  not  compensate  for  a 
drop  in  atmospheric  pressure  of  one-half,  such  as  occurs  when  a 
height  of  18,000  feet  has  been  reached. 

INCREASED  BLOOD  FLOW. 

The  second  method  will  be  more  productive  of  results.  Instead  of 
providing  the  normal  amount  of  blood  with  the  usual  burden  of 
oxygen  an  increased  blood  flow  with  a  lessened  amount  of  oxygen 
per  unit  will  answer  as  well. 


80  MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 

Increased  blood  flow  is  accomplished  in  two  ways.  There  must 
be  peripheral  relaxation  of  the  arteries  to  allow  more  blood  to 
pass,  and  there  must  be  increase  in  the  amount  of  blood  coming  from 
the  heart.  The  latter  is  accomplished  either  by  increase  in  pulse 
rate  (more  beats  per  minute  delivering  the  normal  volume)  or  by 
increase  in  volume  output  per  beat.  Increase  in  heart  output  by 
either  method  would,  of  course,  tend  to  raise  the  blood  pressure. 

It  may  be  emphasized  that  a  very  considerable  increase,  possibjy 
a  doubling,  of  the  blood  flow  may  be  accomplished  with  very  little 
evidence  that  this  is  taking  place,  since  the  various  mechanisms 
for  accomplishing  it  interplay  in  such  a  fashion  as  to  hide  each 
others'  traces.  Thus  increase  of  pulse  may  be  made  unnecessary  by 
increase  of  volume  per  beat  (it  is,  however,  still  a  controversial  ques- 
tion how  much  the  latter  can  vary).  Again,  increase  of  heart  out- 
put must,  of  course,  raise  the  blood  pressure,  while  decrease  in 
peripheral  resistance  (vasodilatation)  lowers  it  again.  We  have 
reason  to  believe  that  for  a  given  organism  a  certain  blood  pressure 
is  optimum,  combining  efficiency  with  economy,  and  that  the  body 
tries  to  keep  to  this  pressure  as  closely  as  possible.  For  this  reason  the 
best  type  of  subject  will  show  almost  no  change  in  either  systolic  or 
diastolic  pressure  until  late  in  the  experiment,  when  the  powers  of 
compensation  are  being  pushed  to  the  limit. 

RELATION  OF  VASOMOTOR  CONTROL  OF  THE  HEART. 

A  thorough  understanding  of  the  interplay  between  heart  and  blood 
vessels  is  necessary  in  order  to  comprehend  the  adjustment  and  fail- 
ures of  adjustment  occurring  on  exposure  to  low  oxygen.  In  every- 
day life  this  interplay  is  constantly  going  on ;  the  better  the  condi- 
tion of  the  heart  muscle  and  of  the  arteries  and  the  better  the  nervous 
control  the  more  successful  will  the  organism  be  in  keeping  up  its 
efficiency.  Every  effort,  such  as  rising  from  a  chair  or  running  for  a 
street  car,  even  every  emotion,  calls  for  increase  of  blood  flow  and 
would  inevitably  give  rise  to  increase  of  blood  pressure  and  extra 
work  for  the  heart  if  vasodilatation  did  not  ease  the  strain  and  at 
the  same  time  allow  the  increased  flow.  A  young  man  with  good 
arteries  can  exert  fairly  violent  muscular  efforts  with  moderate  and 
transitory  rise  in  pulse  and  blood  pressure.  An  older  man,  however, 
whose  arteries  are  less  flexible,  can  not  do  this.  In  his  case  the  blood 
pressure  may  increase  to  a  dangerous  point  because  of  failure  of  the 
peripheral  tone  to  relax.  The  result  of  this  failure  will  be  either  that 
the  heart  is  put  upon  a  dangerous  strain  or  that  the  demands  are 
simply  not  met.  In  the  latter  case  the  organism  will  for  the  time 
being  have  to  run  with  a  deficit ;  hence  loss  of  efficiency  and  symptoms 
of  deficient  circulation  (dyspnea,  cyanosis,  weakness,  etc.). 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  81 

NERVOUS  FACTORS  IN  VASOMOTOR  CONTROL. 

The  nervous  element  in  the  control  of  the  vasomotors  is  of  great  im- 
portance. It  is  well  known  that  the  vasomotor  system  is  the  most 
sensitive  part  of  the  body.  The  slightest  emotion  will  cause  flushing 
or  pallor,  or  even  an  anemia  of  the  brain,  which  leads  to  fainting,  .JThe 
nervous  regulation  is  especially  under  the  influence  of  lack  of  "  con- 
dition vrfforri  VUriOulTclliul^  ,  lack  of 
sleep,  etc.  If  a  man  is  out  of  condition  a  slight  effort  will  cause  twice 
the  rise  in  pulse  and  blood  pressure  that  it  normally  should,  and  this 
rise  will  last  much  longer. 

There  are  observations  to  show  that  purely  nervous  factors,  such 
for  instance  as  great  mental  concentration,  will  cause  a  higher  and 
more  lasting  rise  than  severe  muscular  exertion.  This  is  presumably 
because  in  physical  exertion  vasodilatation  will  provide  for  the  extra 
blood  flow  needed  with  very  little  necessity  for  increasing  the  blood 
pressure.  Where  nervous  tension  is  at  a  high  pitch,  however,  the 
vasomotors  are  certain  to  share  in  this  tension.  Peripheral  resistance 
will  be  high  and  the  blood  pressure  will  be  high  and  sustained.  Pres- 
sures of  200  have  been  observed  in  young  men  as  a  result  of  mental 
work  or  excitement,  and  such  a  pressure  may  last  for  an  hour  or 
more,  often  until  peripheral  relaxation  has  been  brought  about  by 
such  means  as  vigorous  muscular  exercise,  a  hot  bath,  etc.  We  shall 
see  later  that  this  psychic  reaction  of  peripheral  vascular  tension 
(and  of  increased  heart  rate  as  well)  has  a  marked  influence  on  the 
ability  to  withstand  low  oxygen. 

In  the  normal  organism  the  amount  of  blood  flow  will  not  only 
be  regulated  as  to  total  amount,  but  there  will  be  accurate  division    / 
according  to  the  needs  of  the  various  parts  of  the  body. 

The  aviator  is  not  using  his  muscles  to  a  great  extent,  so  does 
not  need  a  great  increase  in  blood  flow  here,  though  the  deficiency 
in  oxygen  is  probably  felt  to  some  extent  in  all  the  tissues  and  the 
blood  flow  to  all  parts  of  the  body  may  nee(J  to  be  increased  some- 
what. Two  parts  of  the  body  however,  must  be  especially  taken  care 
of — the  brain  centers  which  feel  the  want  of  oxygen  and  are  regu- 
lating its  supply  and  the  heart  muscle  which  is  doing  more  than  its 
ordinary  work.  It  is  probable  that  one  important  diiference  between 
the  "  optimum  "  type  and  the  type  who  overcompensates  and  strains 
his  circulation  is  that  the  former  keeps  brain  and  heart  well  sup- 
plied with  blood  but  does  not  flood  the  rest  of  his  body,  while  the 
latter  has  a  marked  increase  of  flow  to  all  parts  and  so  throws  this 
unnecessary  extra  work  upon  the  heart. 

89119—18 6 


82  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

FAILURE  TO   COMPENSATE. 

It  has  already  been  suggested  that  when  circumstances  arise  calling 
for  a  compensation  involving  heart  strain  certain  hearts  will  respond 
with  the  necessary  effort  even  to  their  own  detriment,  while  certain 
others  will  give  up  the  task  at  once  and  allow  physical  inefficiency 
to  result.  The  difference  is  partly  one  of  condition  of  the  heart 
muscle  and  general  physical  tone,  and  partly  of  the  quickness  and 
efficiency  of  the  nervous  reactions  which  govern  the  vital  functions. 
The  same  principle  applies  to  the  whole  body,  even  to  the  person- 
ality, as  well  as  to  the  heart  alone.  One  individual  will  drive  at 
business,  athletics,  etc.,  with  an  intensity  which  brings  success,  but 
often  at  the  cost  of  health ;  another  will  save  his  health  but  lose  the 
game  or  the  business  deal. 

This  conception  is  necessary  in  understanding  the  reaction  to  low 
oxygen.  One  subject  will  compensate  fully  with  strain  if  it  is  neces- 
sary; the  other  will  very  early  give  up  the  effort  and  his  efficiency 
will  be  correspondingly  early  impaired.  Inasmuch  as  the  strain  is 
most  vitally  felt  in  the  circulatory  apparatus  it  follows  that  the  sub- 
jects who  are  most^i^rjpjis_m^justir]g  themselves  to  tlie~^iew~coh- 
d MoirWilT~sh o w  cardiac  exhaustion,  while  those  who  show  early  in- 
efficiency will  not.  Furthermore,  a  man  who  shows  eiu'lv  inefficiency 
can  still  go  on  wiih  the  experiment,  becoming  more  and  more  ineffi- 
cient, but  not  straining  his  heart.  The  man  who  compensates,  in  other 
words,  frequently  gives  out  from  heart  or  vasomotor  exhaustion 
(faints)  while  the  man  who  does  not  so  compensate  may  remain  more 
or  less  in  possession  of  his  faculties  to  a  much  higher  altitude.  This 
result  seems  paradoxical  since  the  former  class  are  individuals  who 
are  physically  far  superior  to  the  latter. 

INSUFFICIENT  COMPENSATION. 

It  is  to  be  assumed,  of  course,  that  no  organism  will  fail  to  make 
any  efforts  to  adjust  itself  to  altered  conditions.  We  have,  however, 
encountered  a  few  individuals  whose  reactions  have  been  almost  nil. 
Such  men  show  no  demonstrable  rise  in  pulse,  no  change  in  blood 
pressures,  and  none  in  respiration.  From  this  one  could  predict  that 
the  psychological  tests  (the  best  criterion  we  have  as  to  the  suffi- 
ciency of  the  compensation)  will  show  early  deterioration.  ffiejiave 
observed  "  complete  inefficiency'5  in  a  few  cases  as  low  as  6,000  feet 
(or  at  the  corresponding  oxygen  percentage) .  Such  men  are  usually 
constitutionally  inferior,  often  undersize,  with  poor  chests,  poor 
color,  clammy,  mottled  hands,  poor  complexion,  etc. 

In  addition  to  these  types  of  constitutional  inferiority  similar  lack 
of  reaction  will  be  shown  by  many  men,  especially  those  toward  mid- 
dle age,  who  have  led  a  sedentary  life,  are  overweight  and  flabby, 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  83 

perhaps  with  fatty  hearts.  In  these  cases  it  might  be  expected  that  a 
good  course  of  physical  training  would  much  improve  their  reactions. 
It  has  long  been  recognized  on  Pike's  Peak  that  the  visitors  of  athletic 
type  and  in  good  training  are  much  less  likely  than  others  to  be  moun- 
tain sick. 

It  is  not  to  be  expected  that  either  of  these  types  will  commonly 
be  found  among  a  class  so  carefully  selected  as  aviators.  Less  degrees 
of  inability  to  compensate,  however,  are  not  uncommonly  found.  All 
these  cases,  of  course,  follow  the  rule  that  the  less  vigorous  the  com- 
pensation the  less  likely  the  subject  is  to  showTieart  sir,-! in. 


THE  "  OPTIMUM  "  TYPE. 

At  the  other  extreme  is  the  "  optimum  "  type  for  aviation,  those 
who  compensate  fully  to  very  great  altitudes,  retaining  their  effi- 
ciency and  yet  doing  this  in  so  accurate  and  economical  a  fashion 
from  the  point  of  view  of  the  circulation  that  there  is  little  or  no 
evidence  of  strain.  When  the  break  comes  (above  25,000  feet  in  the 
low-pressure  tank,  at  from  5.5  to  7  per  cent  on  the  rebreathing  appa- 
ratus) it  comes  with  great  suddenness;  from  almost  full  efficiency 
there  is  a  quick  lapse  into  unconsciousness,  but  still  with  no  circula- 
tory collapse.  There  is  no  loss  of  general  muscular  tone;  the  subject 
remains  sitting  Avith  eyes  open,  stylus  held  firmly  in  hand,  color  full, 
though  of  course  cyanotic,  pulse  full  and  regular,  systolic  and  dia- 
stolic  pressures  maintained.  Recovery  is  almost  instantaneous  on 
return  to  normal  oxygen  pressure  and  is  complete.  The  subject 
usually  refuses  to  believe  that  he  has  not  been  conscious  and  efficient 
throughout.  We  must  attribute  this  unconsciousness  to  direct  action 
of  low  oxygen  on  the  cortical  centers  while  the  circulation  is  still  in 
order. 

CIRCULATORY  COLLAPSE. 

Quite  different  is  the  picture  when  circulatory  failure  has  occurred ; 
cardiac  dilatation,  sudden  collapse  of  vascular  tone,  ashy  pallor,  cold 
sweat,  complete  loss  of  muscular  tone,  so  that  the  subject  always  falls 
from  his  chair.  Recovery  is  slow  and  unsatisfactory;  it  is  often 
an  hour  before  the  man  is  himself  again.  Circulatory  collapse  may 
be  seen  at  any  stage  of  the  experiment,  depending  on  the  amount  of 
strain  preceding  it,  and  occasionally  comes  on  most  unexpectedly. 

HEART  STRAIN.  , 

The  syndrome  of  heart  strain,  followed  by  dilatation  and  fainting, 
is  of  very  great  importance  in  aviation.  We  know  that  fainting  in 
the  air  is  common  and  that  such  an  occurrence  is  practically  always 
fatal.  We  know  also  that  aviators  almost  invariably  develop  in  time 


84  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

a  disabling  "  staleness,"  which  we  strongly  suspect  is  the  result  of  this 
recurring  heart  strain,  and  that  fliers  who  have  "gone  stale"  are 
particularly  sensitive  to  low  oxygen  and  particularly  liable  to  dila- 
tation and  fainting. 

That  heart  strain  is  common  was  shown  during  a  recent  demonstra- 
tion of  the  low-pressure  chamber  to  a  group  of  medical  officers,  men 
certainly  of  average  health,  though  not  in  the  best  of  training.  Five 
men  were  taken  into  the  tank  and  of  these  two  had  acute  heart  symp- 
toms and  had  to  take  oxygen  before  20,000  feet  was  reached.  The 
following  day  five  more  men  underwent  the  test ;  one  had  a  dilatation 
at  14,000  feet,  another  at  16,000  feet,  and  a  third  at  18,000  feet.  In 
other  words,  just  half  of  a  group  of  ordinary  subjects  showed  this 
very  striking  effect.  It  was  interesting  that  in  each  case  the  dilata- 
tion was  demonstrated  by  percussion  while  the  subject  still  felt  per- 
fectly well,  according  to  his  statement,  but  in  each  case  he  began  to 
feel  ill  before  a  minute  had  passed  and  would  have  fainted  if  oxygen 
had  not  been  given  promptly. 

Let  us  summarize  what  has  already  been  said  as  the  incidence  of 
heart  strain;  the  "optimum"  subjects  do  not  show  it,  either  because 
they  have  a  strong  heart  muscle  or  because  their  compensation  is 
made  so  economically  as  to  throw  a  minimum  of  work  on  the  heart. 
The  poor  types  of  reactors  (those  whose  compensation  is  of  low 
grade)  do  not  show  it,  because  their  hearts  are  not  being  asked  to 
overwork.  Subjects  with  defective  heart  muscle  do  not  show  it,  be- 
cause their  hearts  refuse  to  overwork.  Those  who  do  show  it  are 
young  men  of  quick  reaction,  usually  of  excellent  constitution,  though 
often  "  out  of  condition."  Such  subjects  often  have  a  marked  psychic 
reaction  from  the  start,  with  rise  in  pulse  and  blood  pressure,  indicat- 
ing undue  tension  of  the  nervous  system.  When  one  listens  to  the 
heart  it  is  evident  almost  from  the  start  that  this  organ  is  working 
too  hard ;  at  first,  perhaps,  with  plenty  of  reserve,  but  later  the  limit 
is  passed  and  there  is  a  sudden  break. 

What  is  the  essential  difference  between  the  "  optimum  "  type  and 
what  might  be  called  the  "  next  to  the  optimum  type,"  by  which  the 
one  shows  no  circulatory  exhaustion  up  to  the  point  of  unconscious- 
ness while  the  other  breaks?  It  is  partly  strengti^n^jj^ajity  of 
heart  muscle  and  ability  to  stand  strain ;  it  is  partly  a  smooth  work- 
ing of  the  nervous  regulation  of  heart  and  blood  vessels,  including 
•freedom  from  high  nervous  tension ;  it  is  partly  the  ability  to  furnish 
an  abundant  circulation  through  the  coronary  vessels  when  need 
arises.  It  can  be  expressed  in  one  word  familiar  to  physical  trainers, 
Condition."  If  we  knew  just  what  "condition"  means  we  should 
have  the  answer  to  the  question  above. 


Legend 


.0  '; 
IJiast.   B.   1' 


..Pulse 


..Reap,   in  deci).   per  min. ,Sy»t.  B.  P 


-M— M 


:       f...< 


'.    :     : 

_UJUOl 


F.S.D.,      Age:    25-5/12 
Very  high  blood-pressure.     Pulse  high, 

but   falls  at  end  showing  exhaustion. 

Possible   valvular  disease.       Test   should 
be  repeated.       On  this  showing   "Class  D" 


U_LL..LL1J LLL! 


m 

;  i 


fl      Ft?1 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY.  85 

CONDITION. 

We  imagine  the  chief  elements  in  athletic  condition  are  a  strong 
heart  muscle,  a  highly  efficient  coronary  circulation,  and  good  periph- 
eral vasomotor  control.  We  may  guess  that  there  may  be  even  deeper 
factors,  such  as  a  difference  in  the  chemistry  of  the  tissues  allowing 
rapid  metabolism,  and  the  ability  to  generate  energy  rapidly  without 
the  accumulation  of  harmful  end  products.  At  any  rate,  our  work 
strongly  emphasizes  the  necessity  for  keeping  aviators  as  nearly  as 
possible  in  perfect  physical  condition  and  preventing  them  from  fly- 
ing when  they  are  not  so.  We  believe  they  should  daily  be  made  to 
exercise  in  such  a  way  that  the  heart  will  have  to  work  harder,  the 
coronary  vessels  deliver  a  full  volume  of  blood,  the  vasomotors  be 
practiced  in  their  work,  the  respiration  deepened,  and  metabolism 
kept  going  at  an  increased  rate. 

TEMPORARY   INDISPOSITIONS. 

By  "  lack  of  condition  "  we  mean  not  only  "  softness  "  due  to  lack 
of  exercise,  but  many  temporary  indispositions,  such  as  may  follow 
a  bad  cold,  recent  illness,  lack  of  sleep,  overwork,  alcoholic  excess, 
etc.  The  influence  of  such  factors  on  ability  to  withstand  low  oxygen 
was  well  illustrated  by  a  subject  who  had  been  tested  many  times  and 
found  to  be  one  of  the  hardiest  we  had  met  with.  One  day  he  was 
carried  in  the  low-pressure  chamber  to  an  altitude  of  22,000  feet  and 
kept  there  about  15  minutes  with  almost  no  effect  on  his  general  effi- 
>  ciency  or  on  his  heart.  That  evening  he  dined  with  friends,  drank  a 
moderate  amount  of  alcohol,  and  went  to  bed  late.  The  following 
morning  he  felt  rather  giddy  and  had  a  slight  headache.  He  was 
taken  to  18,000  feet  in  the  low-pressure  chamber.  At  this  point  he 
had  reached  complete  inefficiency  by  the  psychological  tests,  was 
rather  cyanotic,  and  examination  of  his  heart  showed  the  left  border 
out  3  or  4  cm.  If  he  had  not  been  given  oxygen  at  once  or  brought 
down  quickly  he  would  have  fainted.  It  was  fortunate  for  him  that 
this  occurrence  took  place  in  the  laboratory  and  not  while  in  an  aero- 
plane thousands  of  feet  above  ground. 

We  can  only  speculate  as  to  whether  such  differences  in  condition 
are  due  to  variations  in  nervous  control  or  whether  they  have  a  basis 
in  the  chemistry  of  the  tissues.  At  any  rate,  such  temporary  lack  of 
condition  is  a  much  more  serious  matter  than  we  are  tempted  to  be- 
lieve. Athletic  trainers  recognize  it  clearly  enough  and  would  not 
allow  such  a  man  to  participate  in  a  game,  not  because  he  would  injure 
himself,  but  because  he  would  not  hold  up  to  the  strain  and  might 
lose  the  game.  In  flying,  where  the  aviator's  life  is  at  stake,  equal 
care  should  be  observed,  to  say  the  least. 


86  MANUAL   OF   MEDICAL  RESEARCH    LABORATORY. 

PHYSIOLOGY  OF  EXERCISE  COMPARED  WITH  AVIATION. 

It  must  be  borne  in  mind  that  the  demand  made  upon  the  heart  in 
aviation  is  widely  different  from  that  of  physical  exercise.  The  most 
obvious  difference  is  that  one  call  is  familiar,  and  we  are  used  to 
meeting  it;  the  other  is  unfamiliar  and  requires  delicate  and  accurate 
reflexes  to  sense  it  and  to  meet  it  properly. 

In  the  body  at  sea  level  the  regulation  of  the  vital  functions  is 
largely  activated  by  carbon  dioxide  or,  more  broadly  speaking,  by 
the  chemical  constitution  of  the  blood.  During  exercise  a  large 
amount  of  CO2  is  produced,  and  at  the  same  time  other  metabolic 
products  find  their  way  into  the  blood,  so  that  respiration  and  cir- 
culation are  stimulated  to  great  activity.  There  is  a  great  margin  of 
safety  in  this  method;  long  before  CO2  and  other  substances  in  the 
blood  have  risen  to  a  toxic  level  the  feeling  of  exhaustion  is  so  in- 
sistent that  further  physical  effort  becomes  almost  impossible.  For 
this  reason  circulatory  collapse  rarely  occurs  as  the  result  of  physical 
exertion. 

In  the  case  of  aviation,  on  the  other  hand,  no  extra  CO2  is  being 
found,  and  the  low  atmospheric  pressure  so  reduces  the  partial 
pressure  of  the  CO2  in  the  blood  that  it  exerts  little,  if  any,  regu- 
latory action.  The  probability  is  that  the  activation  of  the  vital 
centers  in  this  case  ceases  to  be  a  function  directly  of  the  constitution 
of  the  blood,  but  depends  on  the  oxygen  metabolism  of  the  nerve-tissue 
itself.  At  any  rate  the  margin  of  safety  between  the  stimulating  and 
the  paralyzing  effect  of  oxygen-want  is  very  narrow,  and  since  there  is 
no  dyspnea  and  distress  preceding  the  final  collapse,  the  latter  comes 
on  with  no  warning ;  hence  its  terrible  danger  to  the  aviator. 

In  exercise,  again,  there  is  a  natural  check  against  excess  which  is 
lacking  in  exposure  to  rarefied  air.  When  exhaustion  comes  one  is 
forced  to  rest,  thus  terminating  the  extra  work  for  the  heart  and 
giving  a  chance  for  recovery.  In  the  case  of  the  aviator,  however, 
exhaustion  brings  exactly  the  opposite  result.  If  the  heart  falters 
for  a  moment,  not  only  do  the  nerve  centers  run  the  risk  of  exposure 
to  a  paralyzing  anoxemia,  but  the  coronary  circulation  becomes  in- 
sufficient, and  on  the  fullness  of  the  coronary  blood  supply  depends 
the  ability  of  the  heart  to  do  this  work.  Thus  a  vicious  circle  is 
started,  and,  once  the  heart  has  begun  to  fail,  nothing  can  avert 
collapse.  In  exercise  faltering  of  the  heart  means  the  opportunity  to 
recover,  in  aviation  it  means  a  break  in  competence  and  dilatation, 
and  probably  death  if  the  exposure  were  continued. 

FAINTING. 

Before  leaving  the  subject  of  fainting  it  should  be  remarked  that 
this  occurrence  is  common  at  all  altitudes,  even  the  lowest.  It  occurs, 
of  course,  in  ordinary  life  on  the  surface  of  the  earth,  not  as  a  sequel 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  87 

of  heart  dilatation,  but  as  a  vasomotor  neurosis  pure  andginjgle.  Evi- 

_^_     ^       M  — _  _rilLJ,. ,      niim.t'»»  "  irr — ""I — "*^J"* 

dently,  however,  since  it  occurs  so  very  frequently  in  flying  we  can 
not  consider  it  purely  a  neurosis  or  dismiss  it  as  a  psychic  effect. 
We  must  say  rather  that  it  represents  a  demoralization  of  the  vaso- 
motor system  in  its  effort  to  make  the  fine  (even  though  not  laborious) 
adjustments  necessary  to  compensate  for  oxygen  deficiency. 

An  interesting  analogy  may  be  drawn  to  writer's  c.ramp  and  other 
occupational  neuroses,  which  suggests  an  explanation  for  the  occur- 
rence of  vasomotor  phenomena,  such  as  fainting  during  exposure  to 
low  oxygen.  These  neuroses  are  never  found  on  the  long  continuance 
of  fine  muscular  movements  involving  accurate  coordination,  as  in 
writing,  use  of  the  typewriter,  sewing,  playing  a  musical  instrument, 
etc.  On  this  analogy  it  is  easy  to  understand  how  the  constant  deli- 
cate adjustments  demanded  of  the  whole  circulatory  system  during 
repeated  flights  at  ever-varying  altitudes  may  lead  to  demoralization 
of  the  vasomotor  system  even  when  the  actual  strain  is  not  great. 

For  this  reason  we  are  inclined  to  class  fainting  as  a  low-oxygen 
effect  even  when  it  occurs  near  the  earth.  It  is  probable  that  the 
routine  use  of  oxygen  at  the  lowest  altitudes  would  prevent  a  great 
deal  of  the  fainting  in  the  air.  As  our  work  has  progressed  we  have 
become  more  and  more  impressed  with  the  perfectly  definite  effects 
following  exposure  to  altitudes  below  5,000  feet.  These  results  are 
usually  not  observed  at  once,  but  are  cumulative,  and  are  ordinarily 
seen  only  in  aviators  who  have  begun  to  "go  stale."  It  is  not  suffi- 
cient, therefore,  to  bar  a  stale  aviator  from  high  flights;  he  should 
not  My  at  all. 

EFFECTS  ON   PATHOLOGICAL  CASES. 

We  shall  now  consider  rapidly  the  behavior  on  low-oxygen  tests  of 
subjects  with  definite  circulatory  lesions  of  various  types. 

ARTERIOSCLEROSIS. 

Individuals  with  stiff  arteries  give  a  very  characteristic  reaction. 
They  illustrate  very  clearly  that  the  physiological  response  to  low 
oxygen  has  to  begin  at  a  very  low  altitude  in  order  to  preserve  the 
normality  of  the  body.  Such  subjects  will  show  effects  very  early, 
both  by  their  inefficiency  and  by  the  abnormality  of  their  heart 
sounds.  We  have  seen  several  who  were  "  completely  inefficient "  at 
8,000  feet,  while  at  the  same  time  the  heart  rhythm  was  hurried,  the 
first  interval  shortened,  and  the  first  sound  weak  and  valvular. 

The  essential  difficulty  with  stiff  arteries  is  that  they  will  not  play 
their  jjart  smoothly  in  ixringiiifiL  about  mcreasecL  blood  floVatLd^at 
the  same  time  sparing  the  heart.  For~tTns"  reason,  even  In  ordinary 

_|_n    — ' "fr— •••i^^^^^^^^^^^^^JM^—  B^MtWWMmMMIPMMPMBMVV* 

life,  arterioscJCerotics  must  continually  be  having  sudden  marked 
rises  in  blood  pressure,  the  result  of  every  exertion  and  every  emotion. 


88  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

The  extra  strain  thus  thrown  on  the  heart  must  lead  either  to  over- 
work of  that  organ  or  else  to  inefficiency. 

Nothing  illustrates  so  well  this  lack  of  adaptability  of  old  arteries 
as  aviation.  Almost  immediately  the  blood  pressure  rises  sharply. 
(We  have  observed  a  pressure  of  180  in  several  perfectly  healthy  arid 
vigorous  older  men.)  At  the  same  time  the  pulse  accelerates.  This 
strain  has  to  be  carried  by  the  heart  at  a  time  when  the  coronary  ves- 
sels, themselves  sclerosed,  are  not  furnishing  the  heart  muscle  the 
extra  blood  supply  called  for,  and  the  blood  that  does  come  carries 
progressively  less  and  less  oxygen.  Of  course  the  heart  can  not  meet 
the  demand  for  more  blood  supply,  and  the  work  is  simply  not  done. 
Such  hearts  do  not  dilate,  in  our  experience,  because  they  give  up 
the  task  rather  than  overstrain  themselves;  at  any  rate,  we  have 
never  dared  to  carry  such  a  subject  to  a  point  where  there  was  like- 
lihood of  cardiac  dilatation. 

It  is  an  old  aphorism  that  ago  means  only  the  condition  of  tho 
arteries.  It  is  well  recognized  abroad  that  the  best  age  for  the  avi- 
ator is  in  the  early  twenties,  and  'that  the  older  he  is  beyond  this 
point  the  less  efficient  he  is  likely  to  be  in  service.  Our  observations 
with  the  low-oxygen  tests  bear  out  this  strongly  and  suggest  that  the 
explanation  may  lie  in  slight  changes  in  the  arterial  walls  and  mus- 
culature at  a  much  earlier  age  than  it  has  been  supposed  that  such 
changes  can  occur. 

This  statement  does  not  imply  that  there  are  no  men  above  30 
or  even  in  their  forties  who  belong  to  the  "  optimum  "  class,  but  the 
older  a  man  is  beyond  20  the  more  likely  he  is  to  show  the  arterial 
type  of  reaction  to  low  oxygen.  Thus,  many  men  of  about  35  will 
show  a  certain  hypertension  from  the  start,  with  a  constant  rise  as 
the  test  goes  on,  e.  g.,  135,  rising  to  150  to  160.  In  these  cases  the 
heart  muscle  will  carry  the  burden  much  longer  than  in  the  manifest 
arteriosclerotics,  and  there  will  be  normal  psychological  reactions 
achieved  by  heart  strain,  followed  eventually,  in  many  cases,  by  dila- 
tation of  the  heart. 

ARRHYTHMIA. 

The  effect  of  low  oxygen  on  subjects  who  have  any  tendency  to 
arrhythmia  is  very  striking.  Abnormalities  of  the  heart-beat  mech- 
anism invariably  become  exaggerated  to  an  alarming  degree.  An 
occasional  extrasystole,  for  example,  will  occur  more  and  more  fre- 
quently as  the  test  progresses,  until  the  majority  of  the  contractions 
are  of  ectopic  origin  or  until  there  are  considerable  periods  of  ab- 
normal beats  in  series  like  those  of  paroxysmal  tachycardia.  This, 
of  course,  interferes  with  the  efficiency  of  the  circulation,  so  that  these 
subjects  become  very  cyanotic,  very  uncomfortable,  and  fail  early  to 
perform  well  on  the  psychological  tests. 


••••  Pulse  * J<<!<;>.  in  <l<v  il.  jvr  min.        • •  Syst.  B.  P 


R.S.,      Age:    35-11/12 
Type   of  case   cocir.cn  at   subject's   age. 
Good   compensation   but   high  blood-press- 
ure.       Mo   sign  of  exhaustion  to   a  very 
high,  altitude,   but  will   not  wear  well 
in  .service.        "Class  B" 


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TIJ1K  IX  MIXTTKS                                                                                                                                                     V 

CADET. 


Age  22  years,  7  months. 


This  chart  shows  compensation.  There  is  a  fair  response  in  respiration.  There  is  a 
typical  rise  in  pulse  and  systolic  pressure  and  a  controlled  but  rather  rapid  terminal 
fall  of  the  diastolic  pressure.  The  systolic  pressure  is  too  high  for  an  A  rating. 


89-1 


..    Puls 


H. 


-  -,  Kesp.   in  dccil.  per  min. 

.,_ 


..Syst.   B.  P 


I....1  '        '        !        !        '        •        i        '        !        ;        '        !        !        I        '        I  I 

i        I        i        i        ' 

J.K.S.,    Age:    21-1/12 
Chart  jjfr,   April   16,    '16.     Ircedintely 
after   attach  of   influenza.       Poor 
compensation   ana    fainted   at  moderate 
altitude. 

;;  TT~1  "i""' 


1  « 


'"01      S3     45     87     88    10    11    V.'.    K    M    15    \<;    \\    r-    in    -'0    1:1    -.'    !'•',    -I    -'3    •-'<   T,    -*   "-'•'    •'•'*    :'>1    «    "3 


•  Rrsp.   in  decil.   per  min. 


J.F..".,    ~HAPT  #2 

Vay    11,    mfr. 

Sere    niitjerit    a?   Chart   #1 ,    four  weeks 
later. 

Excellent   teit    in  every   particular. 
"Cla<?R   AA" 


LJ_     Li  i.  i  _l_ji_J_L. 


I    A  J/\  I    >"•  4 

"n-H7Ti~-^=rr 


r  i  j 


No.  63. 


CADET. 


Age  21  years,  1  month. 


Left  the  hospital  three  days  ago  where  he  was  laid  up  for  a  week  with  influenza. 
Feeling  fairly  well  to-day,  though  not  up  to  his  usual  form. 

The  first  chart,  (chart  1)  is  typical  of  a  man  out  of  condition,  rather  high  systolic 
pressure,  psychic  rise  in  both  pulse  and  pressure,  followed  by  sudden  faint  at  about 
8  per  cent.  In  this  the  diastolic  pressure  fell  practically  to  zero  ;  the,  systolic  pressure 
and  pulse  also  broke  sharply  as  may  be  seen  by  the  slow  recovery  after  the  experiment 
was  terminated. 

He  was  tested  again  two  weeks  later  (chart  not  given)  and  made  a  very  good  run 
with  the  exception  of  a  rather  high  blood  pressure  (148).  In  this  test,  he  was  not 
completely  inefficient  when  taken  off  at  5.5  per  cent.  After  two  weeks  he  was  given 
a  third  test  (chart  2),  which  entitles  him  to  an  A  A  rating.  The  systolic  pressure 
stays  below  140,  there  is  no  break  in  diastolic,  and  there  is  a  moderate  healthy  rise 
in  pulse. 

This  case  illustrated  the  very  serious  effects  of  temporary  indisposition. 


89-3 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


89 


"Legend  —0., 


tnnio  Pulse 

Pulse  Pressure 


-<•  Resp.  in  decil."  per  min.  <•....«  Syst  B.  P 

Accom.  in  mm.  Convergence  in  mm. 


4  5  6  1  3  8  10  11  12  IS  14  15  16  17  18  19  30  21 


*.    »     r<     013 
TIME  IN  MINUTES 


No.  217.— D.  R. 


CHART  11. 

CADET. 


Age  20  years,  6  months. 


There  was  a  roughening  of  the  first,  heart  sound  heard  before  the  test.  No  demonstrable 
enlargement,  second  sounds  equal.  During  the  test  a  definite  systolic  murmur  developed 
and  the  pulmonic  second  sound  was  accentuated.  There  is  no  doubt  of  the  diagnosis 
of  mitral  insufficiency  well  compensated. 

The  chart  is  typical  of  most  cases  of  valvular  lesions.  The  pulse  is  high  throughout 
the  test.  The  systolic  pressure  is  high  and  uniform.  Diastolic  pressure  begins  to  fall 
between  9  and  10  per  cent,  but  is  in  control  at  all  times.  Respiration  shows  rather  a 
marked  response.  Efficiency  is  well  preserved,  the  psychological  rate  being  A.  This  is 
accomplished  at  the  expense  of  marked  overwork  of  the  heart.  Although  this  is  well 
borne  at  the  present  time,  the  presumption  is  that  the  subject  would  soon  show  the 
effects  of  wear,  and  permanent  damage  to  the  heart  might  easily  result.  Class  D. 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 


Legend 


,..„  — -O.,% 

> — •  Diast.  B.  P. 


i  Pulse  •- —  •  Resp.  in  decil.  per  min.  •....••  Syst.  B.  P 

Pulse  Pressure  Accom.  in  mm.  Convergence  in  mm.. 


110 


icn 


CO 


. 
:•.•,::-::.  ::i:::K:is::;:KK:syK^:n  s:i:::::K::r^:::^:::::::^::::::i; 

.-: 


n     n  .n     Q     1     23     4     S     6     7     8    ,8    10   11   13  13   14  15   16   17   18   19  20  31  33   23  24  25   26  27   28  20   30   31   82   33 

TIMK  IN  MINUTES 

CHART  12. 

No. — . — F.S.D.  CADET.  Age,  25  years  5  months. 

An  unusually  bad  record.  Systolic  pressure  very  high  and  at  the  end  rises  to  210. 
Diastolic  shows  marked  fatigue  though  the  oxygen  percentage  reached  is  not  very  low. 
Pulse  rather  high  at  the  start  shows  very  little  acceleration  later  and  at  about  9  per  cent 
begins  to  fall  rapidly. 

The  heart  sounds  became  roughened,  suggesting  a  valvular  lesion,  which  seems  ex- 
tremely likely  from  the  blood  pressure.  Should  be  studied  further ;  test  should  be  re- 
peated. On  the  showing  of  the  chart  given  the  rating  should  not  be  better  than  D. 


MANUAL  OF    MEDICAL  RESEARCH   LABORATORY. 


91 


— •Diast.  B.  P. 


Pulse  «- — 

Pulse  Pressure . 


--•Resp.  in  decil.  per  min.  •  «..«Syst.  B.  P 

Accom.  in  mm.  Convergence  in  mm. 


n     n    n     o     1     2     3     4     5     6     7     8     8    10   11   12   13   14  15   16   17   18  19  20   21   23   23   24  25   26  27   28   20   30   31   32   g3 

TIME  IN  MINUTES  <£) 

CHART  13. 


No.  163.— H.  B.  R. 


CADET. 


Age,  23  years  5  months. 


An  example  of  compensation  held  to  a  very  low  percentage  with  heavy  circulatory 
strain.  There  is  a  marked  psychic  reaction  in  both  pressure  and  pulse  at  the  start,  but 
this  subsides  somewhat  in  the  first  15  minutes  and  should  not  count  too  much  against 
the  subject.  What  is  against  him  is  the  marked  rise  in  pressure  toward  the  end  (16fi) 
together  with  a  high  pulse  and  falling  diastolic,  which  may  be  interpreted  as  showing 
fatigue  though  no  actual  collapse  occurred.  Class  C.  Holds  his  efficiency  well  but  at 
the  expense  of  severe  heart  strain ;  high  blood  pressure  and  pulse.  Nervous  type. 
Would  wear  out  rapidly  if  used  for  high  work. 

At  the  same  time  it  may  be  remarked  that  these  very  qualities  might  make  him  a 
very  valuable  pursuit  flier  as  long  as  he  lasted. 


92 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


Legend 


, ..     Diast.  B.  P. 


Pulse . Resp.  in  decii.  per  min.   ••--....»  Syst.  B.  P 

Pulse  Pressure  Accorn.  in  mm.  Convergence  in  mm. 


40  ifif  H   t-    - 


H     n    n    p     1     2     J 
TIME  IN  MINUTES 


4567 


9  10  11  12  18  14  15  16  17  18  19  20  31  2'i  23  24  J5  26  27  28  33  30  JH  _32  33 

CHABT  14. 


No.  123.— W.  B.  R. 


CANDIDATE. 


Age,  23  years  2  months. 


Suggestion  of  presystolic  thrill  and  murmur  at  apex  found  before  the  test. 

During  test  these  became  much  more  marked  and  a  systolic  murmur  developed. 
Systolic  pressure  high  from  the  start  and  steadily  increased.  Diastolic  remained  low. 
Note  the  very  marked  early  increase  in  respiration  indicating  great  discomfort  in  breath- 
ing. Became  inefficient  at  a  rather  high  oxygen  percentage.  This  chart  is  char- 
acteristic of  the  way  many  valvular  heart  cases  respond  to  the  test.  He  was  not  carried 
far  enough  to  get  the  circulatory  collapse  that  would  almost  certainly  have  come  as  a 
result  of  the  high  pressure  and  pulse.  Class  B. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


93 


Legend 


•MMIII»       Pulse         "'      Resp.  Ta  deciL  per  mm.    • •     Syst.  U  P 

Diast.  B.  P.  Pulse  Pressure  Accom.  in  mm.  Convergence  in  mm. 


?OP 


3  3-45  6.7  »  8  10  11  12  13  14  5  16  1?  18  10  20.21  22  23  24  20^20  .2T.28  2»  .30  81  32  38 


TIME  IN  MINUTES 


CHART  15. 

CADET". 


No.  82.— D.  H.  O.  CADET".  Age,  24  years  7  months. 

Only  significant  finding  in  history  or  physical  examination  was  a  rather  red  throat. 
Blood  pressure  reclining  120,  standing  132,  after  exercise  146  and  two  minutes  later  138. 
Was  rather  nervous  on  test. 

Pulse  reacts  normally  but  rather  excessively  considering  the  percentage  reached.  Res- 
piration somewhat  full  from  the  start,  but  shows  no  increase.  Systolic  pressure  high 
and  steadily  increases  to  180.  At  this  point  (above  10  per  cent)  the  combination  of 
high  pressure  and  pulse  seems  to  be  more  than  the  heart  can  stand.  There  was  probably 
a  dilatation;  at  any  rate  the  subject  almost  fainted  as  indicated  by  the  fall  in  both 
systolic  and  diastolic  pressures.  A  very  bad  run,  hardly  sufficient  to  rate  C.  The  test 
was  repeated  a  week  later.  At  this  time  the  percentage  reached  was  much  lower  before 
inefficiency.  The  blood  pressure  was  still  a  little  too  high ;  134  rising  to  156.  On  the 
second  run  alone  he  would  be  entitled  to  B,  but  since  he  had  shown  high  blood  pressure 
twice,  very  high  once,  it  was  considered  safer  to  rate  him  C. 


94 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


•  __-»  Resp.  in  decil.  per  min. 
Acconi.  in  mm. 


.  •-.-•Syst.  B.  P. 
Convergence  in  mm. 


8  9  10  11  13  13  14  15  16  17  18  19  20  81.23  23  24  -. 


»     «    «     0     1     3     0 
TIME  IN  MINUTES  . 


9*  3*36.37  37  SJ 


No.  382.— A.  M.  G. 


CHAET  16. 

PILOT. 


Age  25  years,  2  months. 

This  man  is  an  instructor  in  flying  and  has  had  200  hours  of  aviation.  He  feels 
decidedly  stale  and  has  asked  to  be  relieved  of  flying  for  the  present.  Is  afraid  to  go 
up  because  he  has  such  poor  judgment  in  his  present  condition. 

Preliminary  pulse :  Reclining  69,  standing  105 ;  after  exercise  120,  two  minutes 
later  102, 

The  only  abnormal  feature  of  his  test  was  the  slow  but  steady  decrease  in  both 
systolic  and  diastolic  pressures.  He  reached  a  fairly  low  oxygen  percentage  before 
becoming  inefficient.  The  proof  of  staleness  here  is  not  full,  but  the  preliminary  pulse 
reactions  and  the  blood  pressures  during  the  test  are  suggestive. 


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-<     >    10   11    IS  18  14    13    1 

j  .•  i  :n  30  ;ra 

No.  50. 


PILOT. 


Age  31  years,  8  months. 


In  good  health,  but  "  out  of  training,"  and  20  pounds  overweight. 

This  chart  shows  almost  total  failure  to  compensate.  There  is  very  little  change  in 
pulse  or  blood  pressure,  and  the  respiratory  reaction  is  deficient.  For  this  reason  there 
is  early  appearance  of  inefficiency  as  shown  by  the  psychological  characters,  and  he  is 
"  completely  ineflicient "  above  9  per  cent.  Since  there  is  no  circulatory  reaction  there 
is  no  evidence  of  strain.  Class  C.  Because  inefficient  at  a  relatively  low  altitude. 


95-1 


,Krsp    in  decil.  pe 


••Syst.   B.  P 


r- 


L.R.R.,  Age:    20-2/12 
Cadet  was   decidely   "stale."     Fainted    4 

nly   at    a  low  altitude.      "Clas<?  D" 
for  th«   present . 


No.  144. 


CADET. 


Age  20  years,  2  months. 


Is  decidedly  "stale,"  hates  to  go  up  in  the  air  at  all.  Feels  tired  and  depressed  and 
is  discontented  in  the  service  at  present.  Certain  complications  at  home  are  on  his 
mind  a  good  deal. 

This  chart  is  typical  of  a  man  in  poor  physical  and  mental  condition.  He  fainted 
rather  suddenly  at  about  13  per  cent.  Previous  to  this  he  had  shown  little  compensatory 
response,  blood  pressure  too  low  from  the  start,  pulse  rising  slightly  and  respiration 
hardly  at  all  affected.  This  man  might  be  expected  to  faint  at  any  time  during  a 
flight  irrespective  of  elevation. 

No  rating  given  but  for  the  time  being  is  unfit  to  fly  at  all.  Withdrawn  from  flying 
and  recommendation  made  for  furlough. 


95-2 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


95 


O,%  H«HtHt  Pul*«  •_»-._£  Reap,  in  decil.  per  min.      •. j^V^  5 

Diast.  B.  P.  Pulse  Pressure  Accom.  in  mm.  Convergence  m  mm. 


n    n     o     1     2     3     4     5     6     7     8    «    10   11   12  13  14  15   16   17   18   19  20  21   23 
TIME  IN  MINUTES 

CHART  17. 


No.  51— R.  N.  H. 


PILOT. 


Age  23  years,  6  months. 


This  is  another  example  of  poor  compensation.  Very  little  response  in  pulse,  none  in 
systolic  pressure,  very  low  pulse  pressure.  Respiration  increased  but  later  feel  off.  At 
the  end  there  is  a  fall  in  systolic  and  diastolic  pressures  indicating  failure  of  the  cir- 
culatory apparatus  to  continue  even  the  limited  effort  it  is  making.  Psychological  effects 
early.  Class  C.  Becomes  inefficient  at  a  relatively  low  altitude. 


96  MANUAL  OF   MEDICAL  RESEARCH  LABORATORY. 

Sinus  arrhythmia  always  becomes  more  marked  during  the  test, 
but  is  to  be  regarded  rather  as  a  sign  of  youth  and  vigorous  reactions 
than  as  an  abnormality.  It  has  no  clinical  importance  as  far  as  we 
know. 

VALVULAR  DISEASE. 

The  diagnosis  of  valvular  lesions  is  easy  during  the  low-oxygen 
test.  We  have  been  able  to  identify  a  considerable  number  of  cases 
in  men  who  had  passed  rigorous  Army  examinations.  Murmurs  and 
thrills  develop  in  a  surprising  fashion  when  due  to  organic  disease. 
On  the  other  hand,  we  have  observed  a  certain  number  of  presumably 
functional  murmurs  which  did  not  alter  during  the  test  while  the 
heart  continued  to  be  perfectly  normal  in  action. 

The  behavior  of  hearts  with  valvular  lesions  depends  on  their  de- 
gree of  compensation.  If  this  is  poor  and  the  heart  muscle  weak 
they  will  give  up  the  fight  early,  allowing  inefficiency  to  develop ;  at 
the  same  time  there  will  be  marked  cyanosis  and  great  discomfort  in 
breathing,  with  palpitation.  Cases  with  poorly  compensated  mitral 
stenosis  do  especially  badly  and  are  very  uncomfortable. 

A  well-compensated  mitral  inefficiency,  however,  behaves  like  an 
overworking  normal  heart.  Such  hearts  must  have  a  good  quality  of 
heart  muscle  and  good  coronary  circulation  to  remain  compensated 
in  ordinary  life,  and  are  well  used  to  overworking  at  times  to  meet 
the  demands  of  every  day.  They  react  vigorously  to  low  oxygen, 
as  a  rule,  run  a  rather  high  blood  pressure,  an  increased  pulse,  give 
evidence  of  overwork  from  the  start,  and  eventually  dilate  and  give 
out. 

We  believe  that  no  man  with  a  valvular  lesion  should  be  allowed 
to  fly,  no  matter  how  perfect  the  compensation,  not  only  because  of 
the  likelihood  of  immediate  heart  strain,  with  dilatation  and  fainting, 
but  because  in  the  course  of  time  the  cumulation  of  repeated  strains 
will  bring  on  a,  disastrous  condition  of  the  heart.  Cases  have  been 
observed  in  the  service  where  a  heart  originally  well  compensated 
has  eventually  broken  down,  and  the  subject  in  these  cases  is  not  only 
unfit  for  further  flying  but  the  heart  injury  may  be  irremediable  and 
he  may  have  to  look  forward  to  a  life  of  invalidism  and  early  death. 
We  have  seen  two  cases  of  mitral  disease  in  aviators  where  distress 
was  found  to  be  pretty  marked  when  the  plane  rises  to  2,500  feet. 

ATHLETIC    HEARTS. 

"Athletic  hearts "  behave  particularly  badly  under  low  oxygen. 
There  is  still  no  general  agreement  as  to  just  what  this  term  signi- 
fies, whether  it  represents  merely  a  great  hypertrophy  of  the  heart 
which  has  not  receded  or  whether  there  has  been  definite  injury  to 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  97 

the  heart  muscle  by  strain.  The  latter  supposition  is  the  more 
probable,  because  we  know  that  the  normal  body  not  only  possesses 
great  powers  of  increasing  its  various  functions  to  meet  special  calls, 
but  that  the  recession  from  such  unusual  increase  in  tissue  and 
function  is  normally  accomplished  easily  and  safely.  We  must, 
therefore,  assume  on  general  principles  that  the  so-called  "  athletic 
heart "  means  an  injured  heart  muscle,  not  a  subinvolution.  Clin- 
ically the  diagnosis  is  usually  easy :  A  history  of  excessive  athletics, 
especially  rowing  and  distance  running,  a  heart  somewhat  enlarged 
to  percussion,  an  abnormally  heaving  apex  beat,  and  sounds  which  are 
either  notably  loud  and  booming,  or  in  a  later  stage  are  of  poor  and 
valvular  quality.  There  is  usually  an  absence  of  murmurs,  though 
the  dilatation  can  easily  lead  to  a  relative  mitral  leak. 

The  reactions  of  the  athletic  heart  to  low  oxygen  are  always  ex- 
cessive, marked  increase  in  blood  pressure  and  pulse,  but  there  is 
likely  to  be  a  rather  early  loss  of  compensation,  since  the  damaged 
heart  muscle  is  unable  to  carry  the  strain ;  it  will  either  give  up  the 
task  (cyanosis,  inefficiency,  etc.)  or  will  dilate  and  cause  fainting. 

IV.— MANUAL  OF  OTOLOGIC  DEPARTMENT,  MEDICAL  RESEARCH 

LABORATORY. 

1.  INTRODUCTORY. 
MEDICAL  PROBLEMS — OTOLOGIC  RESEARCH  PREVIOUS  TO  THE  WAR. 

Certain  unique  features  concerning  the  study  of  the  ear  in  aviation 
are  worthy  of  special  attention.  Since  our  entrandfe  into  the  war 
the  Medical  Department  of  the  Aviation  Service  has  encountered  cer- 
tain problems  of  ophthalmologic,  cardio-vascular,  respiratory,  psychi- 
atric, and  other  character.  The  work  of  research  into  the  relation 
between  the  motion-perceiving  function  of  the  internal  ear  and  fly- 
ing, however,  had  been  undertaken  long  before  the  entrance  of  the 
United  States  into  the  war.  A  group  of  otologists  had  conducted 
experiments  and  carried  on  investigations  involving  the  end-organs, 
nerve  paths,  and  brain  connections  of  the  vestibular  portion  of  the 
internal  ear  for  a  period  covering  the  preceding  decade.  Many 
months  before  the  United  States  entered  into  the  conflict  several  of 
this  group  of  otologists  had  been  in  correspondence  with  the  Medical 
Department  of  the  United  States  Army  upon  the  subject  of  the 
physical  requirements  of  applicants  for  the  air  fighting  forces,  and 
the  total  available  work  done  upon  both  sides  of  the  Atlantic  was 
macte  the  basis  of  the  standards  adopted  for  these  physical  require- 
ments of  prospective  Army  fliers. 

89119—18 7 


98  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

ARBITRARY   REQUIREMENTS   FIXED   BY   CHIEF   SURGEON,   AIR   MEDICAL 

SERVICE. 

Immediately  after  our  entrance  into  the  war  the  present  Air  Medi- 
cal Service  was  organized.  The  Chief  Surgeon  of  the  Air  Medical 
Service,  when  he  was  confronted  with  the  problem  of  formulating 
a  plan  for  selecting  men  for  training  as  fliers  for  the  Army,  decided 
to  attempt  to  limit  the  admissions  into  this  service  to  men  who  were 
definitely  known,  as  far  as  was  possible  to  determine  by  skilled 
medical  examinations,  to  be  possessed  of  normal  physical  equipment. 

ONLY   PHYSICAL    ITEMS    COVERED    BY    MEDICAL   EXAMINATION. 

The  determination  of 'their  possession  of  all  attributes  other  than 
physical  fell  to  another  division  of  the  Air  Service,  the  Mental 
Examining  Board,  and  at  no  time  constituted  a  part  of  the  work  of 
the  Medical  Service.  The  sole  duty  of  the  Chief  Surgeon  with  respect 
to  the  examination  of  applicants  for  flying  training  was  to  demon- 
strate in  each  man  the  presence  of  normal  physical  equipment. 

FORMATION   OF   STANDARD   BLANK   FOR  PHYSICAL  EXAMINATION. 

For  the  purpose  of  furnishing  a  standard  plan  on  which  these 
physical  examinations  could  be  conducted  upon  a  uniform  basis, 
blank  609,  A.  G.  O.,  was  formulated,  after  consultation  with  the  high- 
est medical  authorities  in  the  various  special  fields  of  medical  work 
covering  the  complete  physical  examination  of  man.  The  /ophthal- 
mologist, the  otologist,  the  rhinolaryngologist,  the  neurologist,  the 
respiratory  anfl  cardiovascular  specialist,  the  gastroenterologist,  the 
orthopaedist,  the  general  surgeon,  the  dermatologist,  the  genito- 
urinary specialist,  are  all  represented  in  the  constitution  of  this 
examination  blank,  and  the  general  field  of  complete  physical  exami- 
nation covered  to  the  satisfaction  of  each. 

PHYSICAL  EXAMINING  UNITS. 

Special  care  was  exercised  to  pick  the  highest  grade  medical  exami- 
ners available  at  each  point  where  it  was  deemed  necessary  to  estab- 
lish a  Physical  Examining  Unit,  and  the  work  of  .each  unit  was  de- 
partmentalized in  the  best  manner  possible  to  render  each  examiner 
capable  of  serving  in  his  most  efficient  capacity. 

No  difficulty  was  encountered  in  securing  the  services  of  men  well 
trained  in  all  special  medical  work  represented  in  this  blank,  with 
the  notable  exception  of  the  examination  of  the  internal  ear.  This 
was  relatively  so  new  that  the  limited  number  of  those  capable  of 
doing  this  portion  of  the  work  rendered  it  necessary  in  establishing 
each  Physical  Examining  Unit,  to  pay  special  attention  to  the  selec- 
tion of  the  otologist.  In  many  instances  it  was  necessary  to  develop 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  99 

the  man  capable  of  handling  this  portion  of  the  work  by  a  special 
intensive  course  of  training  and  instruction. 

DETAILED  INSTRUCTIONS. 

Carefully  detailed  instructions  were  prepared  by  high  authorities 
oipon  the  individual  medical  branches  involved  in  this  special  ex- 
amination, and  these  were  sent  to  each  Physical  Examining  Unit  for 
its  guidance;  from  time  to  time  additional  instructions  were  issued 
by  the  Chief  Surgeon  for  the  purpose  of  further  improving  the  ex- 
amining service ;  special  visits  to  Physical  Examining  Units  were  made 
from  time  to  time  with  a  view  to  maintaining  this  service  at  its  high- 
est efficiency,  and  frequent  consultation  of  the  best-informed  medical 
authorities  on  the  subjects  involved  were  held,  in  attempts  to  omit 
nothing  which  might  improve  the  quality  of  this  work.  Full  ref- 
erence was  made  to  the  accumulated  experience  of  the  Allies;  and 
confidential  and  other  reports  from  medical  officers  in  England  and 
France  were  thoroughly  digested  and  used  to  shape  up  the  service  of 
the  Chief  Surgeon's  examiners. 

IMPORTANT  SENSORY  EQUIPMENT. 

Among  the  applicant's  sensory  equipments  which  were  deemed  im- 
portant to  demonstrate  as  normal  were  visual  perception,  sound  per- 
ception, deep  sensibility  (or  muscle- joint-splanchnic  or  kina3sthetic 
sense),  tactile  sense,  and  motion  perception;  special  examination  of 
olfactory,  taste,  and  certain  other  special  senses,  such  as  cold,  heat, 
pain,  pleasure,  sexual,  tickle,  hunger,  thirst,  nausea,  and  others  were 
not  deemed  of  sufficient  military  importance  to  warrant  special 
scrutiny. 

COMPARISON  OF  GROUND  AND  AIR  SERVICE  CONDITIONS. MOTOR  COORDINA- 
TIONS.  BODILY     ADJUSTMENTS. — IMPORTANCE     OF     SENSES     TO     MOTOR 

ACTS. 

The  difference  between  the  man  on  the  ground  and  the  man  in  the 
air  lies  in  the  fact  that  the  former  can  stand  still,  the  latter  can  not. 
When  the  flier  walks  across  the  field  to  his  plane,  all  his  motor  co- 
ordinations are  concerned  with  maintaining  the  proper  relation  be- 
tween his  body  and  the  element  which  is  supporting  its  weight,  the 
earth.  When  he  straps  himself  in  the  seat  before  flight  he  practically 
straps  wings  to  his  body;  thenceforth,  until  the  end  of  his  flight, 
every  motor  coordination  is  concerned  with  maintaining  a  proper 
relation  with  the  new  element  which  is  supporting  his  weight,  the 
air.  The  only  means  he  possesses  of  adjusting  his  relation  with  the 
new  weight-supporting  element  is  the  plane;  while  flying,  all  motor 
coordinations,  whether  carefully  calculated  or  instinctively  per- 


100  MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 

formed,  are  concerned  exclusively  with  controlling  the  plane.  The 
promptness  and  efficiency  with  which  motor  coordinations  are  per- 
formed depend  directly  upon  the  acuteness  of  sensory  perceptions. 

MOTION    INDISPENSABLE    TO    FLYING. SPECIAL    IMPORTANCE    OF    MOTION 

SENSING. — INTEGRAL  ELEMENTS  IN  MOTION  SENSING. 

Rising  in  the  air  in  an  aeroplane  is  made  possible  only  by  rapid 
motion.  Acuity  of  motion  perception  assumes  much  greater  impor- 
tance to  the  flier  than  to  the  pedestrian,  and  in  order  to  appreciate 
the  full  importance  of  this,  one  must  have  a  clear  conception  of  the 
component  senses  going  to  make  up  motion  perception.  Muscle-and- 
joint  sense,  splanchnic,  visceral  sense,  kinsesthetic  sense — all  grouped 
for  convenience  under  the  term  "  deep  sensibility,"  vestibular  sense, 
vision  and  tactile  sense,  each  participate  in  the  composite  of  gen- 
eral motion  perception. 

DEEP  SENSIBILITY  ON  THE  GROUND  COMPARED  WITH  IN  AIRPLANE. 

The  motion  sensing  of  deep  sensibility  on  the  ground  is  practically 
exclusively  concerned  with  sensing  the  effect  of  the  pull  of  gravity 
upon  the  body ;  in  the  air  it  is  also  concerned  with  sensing  the  effect 
upon  the  body  of  two  other  pulls,  that  of  the  plane's  propeller  and 
that  of  centrifugal  force  on  curves.  Impulses  generated  by  these 
three  pulls  coming  in  via  the  deep  sensibility  tract  must  undergo 
accurate  analysis  in  the  brain  and  be  properly  estimated  and  labeled, 
if  confusion  and  misinterpretation  are  to  be  avoided.  While 
such  analysis  is  accomplished  by  normal  individuals,  it  is  only  at 
the  expense  of  a  certain  amount  of  the  more  accurate  sensing  of  the 
pull  of  gravity.  Whereas  on  the  ground  practically  100  per  cent  of 
this  incoming  information  expresses  gravity  pull,  a  less  percentage 
of  gravity  pull  is  expressed  by  it  in  the  air. 

VISION  ON  THE  GROUND  COMPARED  WITH  IN  THE  AIR. 

Vision,  possibly  the  most  important  of  all  motion-perceiving  senses 
on  the  ground,  suffers  some  impairment  of  its  usefulness  in  the  air 
by  reason  of  the  reduction  in  the  number  of  visible  elements  in  the 
new  environment,  such  as  the  usual  objects  making  up  the  landscape. 
When  darkness  or  cloud  further  reduces  the  utility  of  vision,  this 
sense  becomes  almost  eliminated  as  a  source  of  guiding  information 
to  the  flier. 

TACTILE  SENSE  RELATIVELY  UNIMPORTANT. 

Tactile  sense  contributes  less  than  any  of  the  other  three  senses 
to  motion  perception  on  the  ground ;  to  the  flier,  although  insulated 
by  warm  clothing,  goggles,  gauntlets,  and  helmet,  it  is  still  of  value 
as  a  source  of  guiding  information. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  101 

VESTIBULAR  SENSE,  ITS  MOTION  SENSING  UTILITY  AS  GREAT  IN  THE  AIR  AS 

ON  THE  GROUND. 

Vestibular  sense  suffers  no  depreciation  in  utility  in  the  air  as 
compared  with  on  the  ground.  Its  sole  function  has  always  been, 
and  continues  unaltered  in  any  way  to  be,  pure  sensing  of  motion. 
In  flying,  therefore,  its  function  assumes  a  relatively  greater  impor- 
tance than  that  of  the  other  special  senses  cooperating  with  it  to 
furnish  the  individual  Avith  his  composite  of  knowledge  concerning 
motion. 

In  view  of  the  foregoing,  it  is  apparent  that,  in  flying,  motion  takes 
on  a  much  greater  importance  as  regards  potential  safety  or  disaster 
for  the  individual  than  it  possesses  on  the  ground  and  that  motion 
perception  is  commensurately  of  greater  importance  in  the  air  than 
on  the  ground. 

Regardless  of  the  actual  percentages  which  would  express  the  shares 
of  vision,  deep  sensibility,  vestibular  and  tactile  sense  in  the  total  of 
motion-sensing  on  the  ground,  it  is  established  that  three  of  these  four 
are  reduced  in  efficiency  by  conditions  incidental  to  flying,  and  the 
fourth,  vestibular  sense,  is  not  so  reduced,  and  is  therefore  of  rela- 
tively increased  importance.  It  follows  that  it  is  of  prime  impor- 
tance to  determine  that  men  to  be  trained  as  fliers  possess  normal 
vestibular  apparatus.  So  important  is  it  for  the  flier  to  possess  nor- 
mal vestibular  acuity  of  motion-perception  that  no  man  should  be  per- 
mitted to  begin  training  as  a  pilot  who  has  not  definitely  shown  nor- 
mal reactions  to  vestibular  tests. 

VESTIBULAR  FUNCTION  STANDARD  REQUIREMENTS. 

The  entire  vestibular  apparatus  was  tested  as  carefully  and  as 
accurately  as  the  state  of  our  knowledge  concerning  it  permitted.  It 
was  decided  to  reject  applicants  whose  vestibular  apparatus  gave  evi- 
dence of  motion-sensing  acuity  below  a  certain  degree,  albeit  it  was 
fully  realized,  in  establishing  this  limit,  that  it  in  no  way  represented 
a  line  of  demarkation  between  acuities  of  this  perception  compatible 
with  and  incompatible  with  flying. 

POSSIBILITIES  OF  GREATER  LATITUDE  REALIZED. 

It  was  fully  realized  by  the  Chief  Surgeon  and  his  staff  that  it  is 
possible  for  a  man  to  fly  with  a  vision  of  20/40  or  20/60,  or  with  a 
talipes,  or  with  a  hearing  of  5/40.  The  decision  was  arbitrarily  made, 
however,  that  no  man  would  be  accepted  for  flying  training  by  the 
Army  except  those  with  20/20  vision,  absence  of  gross  malformations, 
40/40  hearing,  and  acuity  of  vestibular  motion-perception  as  repre- 
sented by  a  minimum  of  16  seconds'  nystagmus  and  normal  past- 
pointing  and  falling  responses  to  standard  stimulation. 


102  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

DIFFICULTIES   IN   DECIDING  UPON   ARBITRARY  STANDARDS CONFIRMATION 

OF   WISDOM   OF  ADOPTED   STANDARDS. 

At  the  time  of  the  establishment  of  these  standards  it  was  recog- 
nized as  a  very  difficult  matter  to  state  dogmatically  what  consti- 
tuted the  average  length  of  nystagmus  and  past-pointing.  All  that 
could  be  relied  upon  were  deductions  from  clinical  experiments 
with  a  series  of  healthy  individuals  examined  by  various  observers 
over  a  period  covering  over  10  years  as  contrasted  with  the  impaired 
responses  observed  in  over  a  thousand  pathologic  cases.  It  was 
realized  that  it  was  a  great  responsibility  to  establish  what  should 
be  regarded  as  normal  responses.  It  is  therefore  with  a  great  deal 
of  satisfaction  that  we  publish  at  this  point  the  composite  results  of 
the  turning-chair  test  performed  by  skilled  standardized  otologists 
in  the  examining  units  on  many  tens  of  thousands  of  applicants  for 
the  Aviation  Service.  A  compilation  of  statistics  has  been  made, 
the  digest  of  which,  with  respect  to  responses  in  nystagmus,  past- 
pointing  and  falling,  entirely  confirms  the  judgment  upon  which 
the  original  standards  were  based. 

The  turning-chair  tests  proper,  exclusive  of  the  static  and  dynamic 
tests,  are  cause  for  practically  all  of  the  rejections  in  this  particular 
field,  being  2  per  cent  out  of  a  total  of  2.04  per  cent,  or  2  out  of 
every  100  men  examined.  The  average  duration  of  nystagmus  of 
the  entire  number  of  men  examined  was,  after  turning  to  the  right, 
23.5  seconds;  after  turning  to  the  left,  23.2  seconds.  In  those  who 
qualified,  the  nystagmus,  after  turning  to  the  right  was  23  seconds, 
after  turning  to  the  left,  23.1  seconds. 

The  average  number  of  past-pointings  for  the  total  number  ex- 
amined is  as  follows : 

After  turning  to  right  with  right  arm 3.  8  times 

After  turning  to  right  with  left  arm 3.  7  times 

After  turning  to  left  with  right  arm 3.  8  times 

After  turning  to  left  with  left  arm 3.  7  times 

POSSIBILITY  OF  ALTERATION  IN  ADOPTED  STANDARDS. 

The  Chief  Surgeon  held  himself  in  readiness  to  alter  the  adopted 
physical  standards  at  any  time  evidence  indicating  the  wisdom  of 
so  doing  was  adduced;  realizing  the  wealth  of  available  material 
for  Army  fliers  at  the  start  of  the  formation  of  the  United  States 
Flying  Corps,  it  was  deemed  best  to  maintain  the  highest  standards 
until  it  became  apparent  that  a  change  was  for  the  best  interests  of 
the  service. 

FALLIBILITY  OF  ENTRANCE  EXAMINING  SERVICE. 

The  physical  examinations  of  applicants  were  carried  out  at  67 
Physical  Examining  Units,  32  of  which  were  constituted  by  Army 


MANUAL  OF   MEDICAL  RESEARCH.  LABORATORY.  103 

medical  men  in  various  camps.  As  was  to  be  expected,  a  certain 
amount  of  evidence  of  the  fallibility  of  these  examinations  has  come 
to  light.  Certain  men  have  been  encountered  in  the  Air  Service  who 
were  physically  unfit,  and  certain  others  have  been  rejected  who 
were  physically  fit.  Considering  the  magnitude  of  the  task,  how- 
ever, a  review  of  the  results  of  the  examinations  of  a  hundred  thou- 
sand applicants  in  nine  months  reveals  a  performance  on  the  part 
of  these  examining  units  which  is  satisfactory  to  the  Chief  Surgeon. 

2.  EAR,  NOSE  AND  THROAT  KEQUIREMENTS. 

DETAILS  REGARDING  EXAMINATION  OF  QUESTIONS  OF  BLANK  609,  A.  G.  O., 
FROM  13  TO  21,  NOT  INCLUDING  20,  WHICH  HAS  ALREADY  BEEN  TOUCHED 

UPON. 

13.  History  of  ear  trouble — 

(a)  Ever  have  ringing  or  buzzing  in  either  ear,  earache,  dis- 
charge, or  mastoiditis? 

(&)  Ever  have  attacks  of  dizziness  from  any  cause? 
(c)  Ever  been  seasick?     If  so,  how  often  and  how  long  does  it 

last? 
(d)  Ever  had  a  severe  injury  to  head? 

The  answers  to  question  13  are  merely  designed  in  a  general  way  to 
arrive  at  an  indication  of  any  previous  ear  trouble.  It  is  to  be  taken 
into  consideration  that  very  few  candidates  are  willing  to  admit  the 
history  of  ear  discharge  or  dizziness,  and  conclusions  will  have  to  be 
drawn  from  the  examination  of  the  drumhead  and  subsequent  hearing 
and  rotation  tests. 

It  is  the  universal  experience  that  all  candidates  deny  that  they 
have  ever  been  seasick,  thinking  thereby  to  prove  that  they  would  be 
unaffected  by  the  motion  of  an  aeroplane.  Answers  to  this  question 
for  that  reason  must  be  taken  with  considerable  allowance.  It  is  to 
be  emphasized  that  it  would  be  improbable  for  a  person  with  per- 
fectly normal  ears  not  to  become  seasick  upon  his  first  exposure  to  a 
rough  sea. 

14b.  Appearance  of  membrana  tympani. — A  perforation  of  the 
drumhead,  unless  transitory,  is  to  be  regarded  as  a  cause  for  rejection. 
If  the  drumhead  is  excessively  thin  and  scarred,  even  if  the  hearing  is 
normal,  the  applicant  should  be  rejected.  Experience  has  shown  that 
even  in  the  low-pressure  chamber  of  the  laboratory  perforations  can 
easily  occur  in  such  drums  by  a  rapid  descent. 

Pathological  conditions  of  the  internal  ear  disqualify.  Acute  or 
chronic  disease  of  the  middle  ear  disqualifies,  except  that  reexamina- 
tion  after  full  recovery  may  be  made  the  basis  of  subsequent  accep- 
tance. Moderately  retracted  drumhead,  loss  of  light  reflexes, 
thickened  drum  membrane,  and  chalk  deposits  do  not  disqualify  pro- 


104  MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 

vided  the  hearing  is  normal.  The  pathology  of  the  drumhead  is  not 
an  index  of  the  hearing  ability.  No  conclusions  can  be  drawn  without 
hearing  tests. 

15  to  18.  Nasopharynx. — This  region  must  be  carefully  examined. 
If  defect  can  be  removed  by  operation,  this  should  be  required  prior 
to  acceptance.  If  nonoperable  or  operation  is  refused,  it  is  a  cause 
for  rejection. 

The  question  as  to  what  degree  of  deviation  of  the  septum  demands 
an  operation  is  a  difficult  one  to  answer  and  must  be  left  to  the  ex- 
perience of  the  examiner.  One  thing  must  always  be  clearly  borne 
in  mind;  aside  from  the  straightening  of  an  occlusive  deviation  for 
the  purpose  of  giving  the  candidate  better  air,  resecting  the  septum  is 
not  infrequently  of  great  value  as  a  prophylactic  measure.  The  ma- 
jority of  individuals  who  have  trouble  with  their  ears  are  troubled 
because  of  a  postnasal  and  Eustachian  tube  catarrh.  Septal  devia- 
tion far  back,  impinging  on  the  inferior  turbinate  and  acting  as  a 
continual  irritant  to  the  nasopharynx,  should  be  corrected.  Cases 
of  marked  deviation  which  have  led  to  atrophic  condition  of  the 
mucus  membranes  do  not  necessarily  require  operations.  The  prime 
object  is  to  prevent  acute  postnasal  trouble  which  might  come  on  as 
a  result  of  exposure,  rather  than  to  attempt  to  obviate  an  insidious 
middle-ear  catarrh  which  might  have  come  on  in  later  life. 

The  nares  should  be  most  carefully  examined  for  any  signs  of  acces- 
sory sinus  diseases.  Even  a  suspicion  of  this  condition  should  lead 
to  a  most  careful  and  painstaking  examination,  including  properly 
taken  X-ray  stereoscopic  photographs. 

16.  Condition  of  tonsils  and  history  of  attacks  of  tonsillitis. — The 
diagnosis  of  diseased  tonsils  is  a  difficult  one  and  must  be  left  largely 
to  the  experience  of  the  individual  examiner.  Candidates  are  disin- 
clined to  admit  a  history  of  sore  throats.  It  must  not  be  forgotten 
that  probably  80  per  cent  of  the  sick  calls  on  the  other  side  is  made 
up  of  sore  throats.  Soldiers  who  never  complain  of  throat  trouble 
in  this  country  when  they  are  subjected  to  the  exposures  incidental 
to  field  service  rapidly  develop  inflammatory  throat  conditions,  which 
disqualify  temporarily  for  duty.  One  should  be  cautious  in  declaring 
a  tonsil  healthy.  All  throats  should  be  examined  under  good  illumi- 
nation ;  attempt  to  express  contents  of  crypts  should  be  made,  and  if 
questionable  matter  can  be  squeezed  out  the  tonsils  should  be  removed. 
Buried  tonsils  in  which  the  anterior  pillar  is  affected  should  be  re- 
moved, as  should  the  hypertrophic  type.  The  experience  in  this  lab- 
oratory has  been  that  in  spite  of  the  fact  that  all  candidates  were 
originally  examined  by  throat  specialists,  many  when  reexamined  in 
this  institution  showed  diseased  tonsils.  Our  general  impression  is 
that  it  is  better  to  err  slightly  on  the  side  of  radicalism  in  regard  to 
operation  on  the  tonsils  for  those  about  to  enter  active  military  service. 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY.  105 

Examination  of  the  teeth  must  not  be  neglected.  It  must  never  be 
forgotten  that  crowned  teeth,  pyorrhea,  and  alveolar  infections  may 
be  the  sources  of  much  toxemia.  Special  attention  should  be  given 
to  this  matter,  and  if  there  is  any  doubt  in  the  mind  of  the  examiner 
as  to  the  condition  of  the  candidate's  teeth  he  should  be  instructed  to 
have  his  mouth  put  in  good  shape  before  finally  passing  him. 

17.  Adenoid  tissue  is  very  common  in  children  and  increases  in  size 
from  birth  to  the  age  of  6  years  and  then  normally  subsides  about  the 
age  of  puberty.    One  does  not  expect  to  find  much  adenoid  tissue  in 
adults.    Adenoids  do  their  harm  early  in  life,  and  this,  as  far  as  it 
concerns  this  examination,  is  evidenced  by  deformed  jaws,  misshapen 
noses,  and  poor  hearing.    Adenoid  tissue  in  the  adult  is  easily  seen 
with  a  post-nasal  mirror,  the  digital  examination  being  unnecessary. 

18.  The  condition  of  the  Eustachian  tubes  is  one  of  vital  importance. 
Generally  speaking,  it  can  be  said  that  if  the  candidate's  drumhead 
and  hearing  are  normal  the  Eustachian  tube  is  probably  in  good  con- 
dition.    In  addition,  regulations  require  that  the  patulence  of  the  tube 
should  be  demonstrated  by  the  auscultation  tube  during  inflation  by 
means  of  Politzerization  or  catheterization.    The  former  procedure 
is  ample  for  all  practical  purposes.    If  tubal  troubles  are  of  such  a 
nature  as  to  demand  it,  an  examination  should  be  made  with  some 
good  pharyngoscope. 

STIMULATION    OF    END-ORGANS. RESULTS    SENSORY,    MOTOR. — VERTIGO. — 

KIND  OF  MOTION  USED  AS  STIMULUS. 

20.  Vestibular  tests. — The  motion-perceiving  apparatus  of  the  in- 
ternal ear  is  subjected  to  stimulation  by  motion  of  certain  standard 
quantity  and  quality,  and  the  results  are  observed  according  to  uni- 
form standard  methods.  Two  results  are  noted — a  sensory  result,  the 
subjective  sensation  of  motion,  and  a  motor  result,  involuntary  move- 
ment of  the  eyes.  When  the  subjective  sensation  of  motion  is  in 
accord  with  fact,  we  call  it  normal  sensing  of  motion ;  when  it  is  not 
in  accord  with  fact,  we  call  it  "vertigo."  The  only  difference  be- 
tween normal  perception  and  vertigo  lies  in  the  sensing  of  motion 
being  in  accord  with  or  contrary  to  fact.  The  most  practical  means 
of  applying  motion  stimulus  is  by  the  rotating  chair,  inasmuch  as 
the  application  of  motion  in  a  linear  direction,  for  the  period  of 
time,  and  in  the  intensity  necessary  to  elicit  certain  standard  responses 
to  that  stimulus  would  necessitate  apparatus  entirely  too  bulky  to 
be  susceptible  of  practical  application  under  ordinary  conditions  of 
office  examination.  By  making  use  of  a  rotational-motion  stimulus 
instead  of  a  linear-motion  stimulus  it  was  possible  to  work  out  a 
standard  means  of  applying  motion  stimulus  in  certain  definite  qual- 
ity and  quantity  in  a  manner  and  by  means  of  an  apparatus  easily 
handled  in  an  office.  For  this  reason  only  the  subject  of  the  tests  of 


106  MANUAL  OP   MEDICAL  RESEARCH   LABORATORY. 

the  vestibular  apparatus  is  made  to  experience  rotational  vertigo. 
An  additional  advantage  in  using  the  rotating  chair  is  that  it  applies 
motion  stimulus  of  a  character  to  produce  a  more  enduring  stimula- 
tion of  the  end-organs  of  the  semicircular  canals. 

Motion  in  a  linear  direction  applied  to  a  fluid  contained  in  a  closed 
semicircular  canal  is  physically  incapable  of  setting  up  a  flow  of  that 
fluid,  just  as  rotational  motion  applied  to  a  fluid  contained  in  a 
straight  canal  can  not  set  up  a  flow. 

NYSTAGMUS. 

/. 

Ewald's  experiment  long  ago  determined  that  involuntary  pulling 
of  the  eyes  in  a  certain  definite  direction  and  plane  occurs  during 
the  time  the  fluid  in  a  normal  semicircular  canal  is  made  to  flow 
in  one  direction ;  and  during  the  time  this  fluid  is  made  to  flow  in  the 
opposite  direction  involuntary  pulling  of  the  eyes  in  the  opposite 
direction  occurs.  By  applying  rotational  motion  it  is  possible  to  re- 
produce Ewald's  experiment  in  effect,  as  a  test  of  eye  reactions  to 
vestibular  stimulation;  and  when  the  character  and  intensity  of 
rotational  stimulus  is  standardized,  comparisons  of  the  results  can  be 
made  and  a  normal  eye  reaction  determined.  This  motor  expression 
of  motion  stimulation  is  nystagmus. 

MEASURING      VERTIGO — VOLUNTARY      TESTIMONY INVOLUNTARY      TESTI- 
MONY  TECHNIQUE — POINTING        TEST STANDARD       TECHNIQUE         OF 

POINTING  TESTS. 

The  normal  man  experiences  a  sensation  of  vertigo  for  between 
15  and  40  seconds  after  being  turned  according  to  standard  tech- 
nique. Evidence  of  this  subjective  sensation  may  be  had  by  volun- 
tary or  involuntary  testimony ;  voluntary  testimony,  such  as  "  I'm 
turning  to  the  right,"  "  I'm  still  turning  to  the  right,"  etc.,  during 
the  persistence  of  the  subjective  sensation;  involuntary  testimony, 
such  as  pointing  test  and  falling.  Standard  tests  make  use  of  invol- 
untary testimony  in  all  cases;  occasionally  this  is  amplified  by  vol- 
untary testimony  with  advantage.  In  observing  the  pointing  before 
turning,  a  very  important  element  in  the  test  can  be  injected  by  im- 
planting in  the  mind  of  the  applicant  the  definite  idea  that  he  is  to 
attempt  to  determine  the  location  in  space  of  the  observer's  finger 
solely  by  registering  in  his  memory  the  location  of  it  according  to 
his  tactile  sense.  This  can  be  augmented  by  having  him  touch  the 
observer's  finger  in  more  than  one  position,  as,  for  instance,  directly 
in  front  of  the  right  hand,  come  back  and  touch;  then  locate  again 
30  degrees  outward  and  come  back  and  touch;  the  same  procedure 
in  front  of  the  left  hand.  This  implants  in  his  mind  the  funda- 
mental idea  of  being  able  to  orientate  himself  solely  by  means  of  in- 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  107 

formation  coming  from  his  tactile  end-organs.  After  standard  rota- 
tion to  the  right,  for  example,  normal  man  experiences  a  certain  very 
definite  vertigo,  a  subjective  sensation  of  turning  to  the  left  in  the 
same  plane  as  the  rotation  for  a  normal  period  of  time.  If  the  point- 
ing test  is  carried  out  during  this  period  of  vertigo,  instead  of  suc- 
ceeding in  pointing  accurately  to  the  testing  finger  he  executes  the 
pointing  in  accordance  with  his  subjective  sensation  of  motion.  Feel- 
ing that  he  is  turning  definitely  away  from  the  testing  finger  to  the 
left,  for  example,  he  reaches  for  it  to  the  right.  This  is  normal  past- 
pointing. 

INSULATION  OF  SUBJECT. 

The  insulation  of  the  applicant  during  this  test  should  be  as  per- 
fect as  possible.  A  black  domino  mask  should  be  used,  absolute 
quiet  should  be  maintained,  olfactory  impressions  should  be  shunted 
out,  and  he  should  be  left  as  solely  as  possible  dependent  upon  the 
information  brought  to  him  along  the  vestibular  tract  alone. 

SIGNALING   SUBJECT OBVIATING  SEARCH    MOVEMENTS — OBSERVING   PAST- 
POINTING- — HOW  TO  CONSTRUE  COMPENSATORY  POINTING. 

The  applicant  should  be  definitely  instructed  before  turning  that 
he  should  not  expect  a  verbal  order  to  touch  the  observer's  finger, 
raise  his  hand  and  come  back,  and  attempt  to  find  it  after  the  turn- 
ing; he  should  be  practiced  before  turning  in  executing  his  touch, 
raising  his  hand,  and  coming  back  to  find  the  finger  upon  receipt  of 
the  signal  from  the  observer's  finger  as  it  comes  into  the  position 
which  it  maintains  during  the  test — the  observer  bringing  up  his 
finger  into  position  so  as  to  tap  the  applicant's  finger  as  a  signal  for 
him  to  execute  his  pointing  without  verbal  command.  It  is  very 
important  for  the  applicant's  finger  to  find  a  finger  of  the  observer 
when  he  comes  down  in  search  of  the  finger  which  is  testing  him. 
Otherwise,  there  is  injected  into  his  mind  a  disconcerting  element  of 
dissatisfaction  in  having  failed  to  find  the  finger  for  which  he  was 
searching.  For  this  purpose  the  index  finger  of  the  observer's  left 
hand  can  be  held  in  readiness  to  furnish  the  touch  necessary  to  shunt 
out  this  sense  of  failure.  In  observing  the  past-pointing  after  rota- 
tion, the  observer's  right  index  finger  should  be  definitely  fixed 
against  the  observer's  hip-  so  that  visual  attention  to  it  on  the  part  of 
the  observer  can  be  dispensed  with,  the  hip  rest  insuring  its  remain- 
ing definitely  where  it  was  when  the  applicant  first  touched  it  in 
making  the  pointing  test.  The  observer's  eyes  can  be  free  to  watch 
the  applicant's  finger  at  the  top  of  the  swing.  Past-pointing  at  the 
top  of  the  swing  is  just  as  definitely  normal  past-pointing  as  at  the 
completion  of  return  to  touch.  Many  cases  compensate  after  evincing 
a  normal  tendency,  let  us  say,  to  past-point  outward  with  the  right 
hand  when  they  should  do  so,  and  subsequently  execute  a  compensa- 


108  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

tory  touch  or  inward  pointing  at  the  bottom  of  the  return.  In  such 
cases  the  pointing  should  be  registered  as  that  executed  at  the  top  of 
the  swing,  which  is  the  primary  and  clean  response  before  it  has  been 
altered  by  the  subconscious  or  conscious  compensation  effected  by 
other  mental  processes.  Visual  attention  on  the  part  of  the  observer 
to  the  applicant's  hand  at  the  beginning  of  his  downward  pointing 
is  of  enormous  importance  and  it  should  be  very  carefully  observed 
as  part  of  the  standard  technique. 

FALL  TEST. 

The  fall  test  is  similar.  A  normal  man,  on  attempting  to  sit  up- 
right after  leaning  forward  during  right  rotation,  feels  that  he  is 
turning  to  the  left,  for  instance,  and  so  gives  involuntary  expression 
to  this  sensation  by  falling  to  the  right  on  attempting  to  assume  an 
erect  sitting  posture. 

These  tests  can  be  completed  in  less  than  five  minutes.  Inci- 
dentally, these  tests  are  in  no  sense  severe  and  are  in  fact  seldom 
regarded  even  as  unpleasant. 

Occasionally  nausea  occurs  after  these  turnings ;  it  is  then  merely 
necessary  to  stop  the  examination  for  the  time  being  and  to  com- 
plete the  remainder  of  the  tests  after  an  interval  of  half  hour. 
There  is  no  need  whatever  to  make  these  tests  in  any  way  distressing 
to  the  candidate. 

OBVIOUSLY  UNFIT  CASES — BORDER-LINE  CASES — CALORIC  TEST DETAILS — 

ALLOWABLE  LATITUDE DRUMHEAD   INSPECTION. 

With  respect  to  the  internal  ear  motion-sensing  apparatus,  its 
nerve  paths  and  brain  connections,  these  turning  tests  quickly  sepa- 
rate the  obviously  fit  from  the  unfit.  The  majority  of  the  candidates 
show  normal  responses;  no  further  testing  is  required,  and  they 
therefore  qualify  and  are  accepted.  Some  candidates  show  such 
markedly  subnormal  responses  that  they  are  immediately  disqualified 
and  rejected.  A  limited  number  give  what  might  be  termed 
"border-line"  responses;  the  question  then  arises.  Has  this  particu- 
lar applicant  sufficient  motion-sense  to  become  an  aviator?  It  is 
here  that  the  caloric  test  is  useful.  The  turning  has  tested  both  the 
right  and  left  ears  simultaneously.  The  caloric  method  enables  us 
to  test  each  ear  separately.  Water  at  68°  F.  is  allowed  to  run  into 
the  external  auditory  canal  from  a  height  of  about  3  feet  through  a 
stop  nozzle,  with  the  head  tilted  30°  forward,  until  the  eyes  are 
seen  to  jerk  and  the  individual  becomes  dizzy.  The  length  of  time 
from  the  beginning  of  the  douching  until  the  jerking  of  the  eyes 
becomes  apparent,  or  until  the  applicant  says  he  is  dizzy,  is  accu- 
rately measured  by  a  stop-watch.  The  type  of  nystagmus  is  then 
noted.  With  head  in  upright  position,  it  should  be  rotary  and  the 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  109 

direction  of  the  jerk  should  be  to  the  side  opposite  the  ear  douched. 
The  length  of  the  douching  shown  by  the  stop-watch  in  the  normal 
is  40  seconds.  The  eyes  are  then  closed  and  the  past-pointing  is 
taken.  The  head  is  then  immediately  inclined  backward  60°  from 
the  perpendicular  (or  90°  from  the  original  position).  There  should 
then  appear  a  horizontal  nystagmus  to  the  side  opposite  to  the  ear 
douched.  The  eyes  are  then  closed  and  the  past-pointing  is  taken 
with  the  head  in  this  position.  The  left  ear  is  then  douched  and 
the  same  procedure  carried  out.  If  the  caloric  test  applied  to  one  of 
these  "border-line"  cases  shows  only  a  slight  impairment  of  the 
responses  from  each  ear,  the  candidate  is  qualified.  If  instead  of 
40  seconds  of  douching,  there  was  required  not  more  than  90  seconds 
of  douching  to  elicit  normal  responses,  the  applicant  is  not  rejected. 
Care  should  be  taken  to  be  certain  that  the  cold  water  is  reaching 
the  drumhead  during  this  caloric  test,  as  wax  or  other  obstruction^ 
in  the  external  canal  would  interfere  with  the  responses  in  a  per- 
fectly normal  individual. 

After  carefully  considering  the  foregoing  the  neurologist  and  the 
general  diagnostician  can  not  fail  to  be  struck  with  the  compre- 
hensive character  of  these  vestibular  tests,  for  frequently  they  are 
looked  upon  as  ear  tests  only.  Six  months  ago  one  of  the  greatest 
otologists  of  Europe  in  discussing  these  tests  raised  the  question  as 
to  the  necessity  or  advisability  of  including  in  aviation  examinations 
the  past-pointing  and  falling  tests,  his  contention  being  that  in  test- 
ing nystagmus  only,  one  secures  definite  evidence  of  the  functional 
state  of  the  semicircular  canal  end-organs  of  the  internal  ear.  When 
his  attention  was  drawn  to  the  fact  that  in  testing  the  past-pointing 
and  falling  in  addition  to  the  nystagmus  one  establishes  definitely 
the  functional  intactness,  (1)  of  the  various  afferent  paths  and 
the  mtracranial  structures  through  which  they  pass,  (2)  of  the 
cerebral  cortical  centers  and  their  transcortical  association  tracts, 
(3)  the  efferent  cerebral  paths  and  the  nuclei  through  which  they 
pass,  (4)  the  cerebellar  nuclei  and  correlation  paths  to  and  from 
cerebellar  cortical  centers,  (5)  various  portions  of  Pons  and  Medulla 
Oblongata,  his  attitude  was  completely  changed  and  he  became  a 
firm  advocate  of  the  complete  testing  of  nystagmus,  past-pointing 
and  falling  as  a  routine  procedure. 

It  can  not  be  emphasized  too  strongly  that  the  vestibular  tests 
are  not  only  ear  tests ;  in  addition  they  actually  test  very  extensively 
a  large  portion  of  the  central  nervous  system. 

Certain  infectious  diseases  are  known  to  manifest  a  predilection  to 
attack  the  vestibular  apparatus.  Acute  toxic  end-organ  disease  and 
neuritis  of  the  VIII  nerve  are  well  recognized  complications  of 
mumps,  typhoid,  and  some  of  the  commoner  epidemic  infections; 
syphilis  is  particularly  prone  to  attack  the  VIII  nerve.  Permanent 


110  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

impairment  of  function  of  the  vestibular  apparatus  in  varying 
degrees  ensues  upon  any  such  attack.  It  therefore  becomes  neces- 
sary to  reexamine  fliers  at  regular  intervals  in  order  to  make  cer- 
tain that  no  functional  deterioration  of  the  vestibular  apparatus 
has  taken  place.  Regular  examinations  should  be  made  at  intervals 
of  about  eight  weeks.  Special  examination  should  be  made  at  once 
of  any  flier  who  manifests  unusual  failure  to  negotiate  air  maneuvers 
with  ordinary  skill. 

3.  OTOLOGIC  PROBLEMS  UNDER  CONSIDERATION  AT  THE  MEDICAL 
RESEARCH  LABORATORY. 

The  first  otologic  problem  attacked  in  the  Medical  Research  Labor- 
atory was  the  effect  of  low  oxygen  on  the  phenomena  of  nystagmus 
and  past-pointing.  It  has  been  demonstrated  by  the  cardiovascular 
and  physiological  departments  that  deleterious  effects  of  low  oxygen 
are  noted  in  connection  with  the  cardiovascular  and  respiratory 
systems.  As  was  to  be  expected,  before  low-oxygen  effects  on  the 
internal  ear  motion-sensing  apparatus  could  be  demonstrated,  cardio- 
vascular and  respiratory  effects  became  manifest.  Therefore,  it  has 
thus  far  been  difficult  to  carry  these  ear  tests  to  a  satisfactory  con- 
clusion. In  these  examinations  the  rotating  chair  was  placed  in  the 
low-presure  tank  with  the  subject  and  observers.  After  having  at- 
tained a  height  of  5,000  feet,  the  candidate  was  exposed  to  the 
effects  of  this  altitude  for  5  minutes,  when  the  routine  nystagmus  and 
past-pointing  experiments  were  carried  out.  The  same  procedure 
was  repeated  at  varying  altitudes  up  to  18,000  feet.  These  findings, 
reported  in  detail  in  another  article,  showed  no  consistent  variations 
from  the  responses  obtained  at  sea  level.  We  may,  therefore,  with  a 
fair  degree  of  safety  assume  that  at  altitudes  up  to  18,000  feet  no 
marked  changes  in  this  function  of  the  internal  ear  occur  as  the 
result  of  low  oxygen.  The  cochlear  portion  was  similarly  unaffected 
at  these  altitudes. 

During  these  experiments  abundant  opportunity  was  afforded  to 
examine  a  large  number  of  drumheads — both  of  the  candidates  and  of 
the  observers.  Experimental  work  in  the  laboratory  has  confirmed 
the  practical  observations  of  fliers — that  middle-ear  difficulties  oc- 
cur during  descent  rather  than  ascent.  One  point  has  been  estab- 
lished without  question,  that  the  amount  of  injection  of  .the  drum- 
head is  directly  proportionate  to  the  degree  of  patulence  of  the 
Eustachian  tube.  Intense  pain  in  the  middle  ear  and  down  the  neck 
was  experienced  by  many  subjects,  who  showed  on  examination,  to 
have  moderate  or  severe  congestion  of  the  naso-pharynx.  One  case 
was  extremely  illuminating  and  shows  that  we  must  not  conclude 
that  because  atrophic  rhinitis  is  present,  the  tubes  must  necessarily 
be  patulous.  One  of  the  examining  medical  officers  had  extremely 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  Ill 

atrophic  and  badly  retracted  drumheads  with  scars  from  repeated 
suppurative  attacks.  A  rapid  descent  produced  a  double  bilateral 
perforation,  the  perforations  evidently  occurring  on  the  sites  of 
former  perforations.  A  sharp  stabbing  pain  was  felt  as  the  observer 
dropped  rapidly  from  14,000  to  1,000  feet,  and  an  examination 
showed  a  bright  red  circle  of  tiny  blood  vessels  surrounding  the  pin- 
point perforations.  The  subsequent  healing  was  uneventful. 

One  of  the  observers,  who  had  a  history  of  repeated  attacks  of 
suppurative  otitis  media  in  early  childhood,  developed  a  typical 
acute  purulent  otitis  media  after  several  ascents  in  the  low-pressure 
chamber  on  three  consecutive  days. 

One  of  the  foremost  otologic  problems  constantly  before  the  chief 
cf  the  Air  Medical  Service  has  been  how  much  leeway  can  be  safely 
allowed  in  standard  tests  of  vestibular  functions  and  acuity  of  per- 
ception. As  has  been  mentioned  before,  all  motor  coordinations 
made  by  the  flier  during  flight,  whether  carefully  planned  and  con- 
sciously performed  or  instinctively  and  subconsciously  executed, 
have  only  one  ultimate  expression,  namely,  the  determining  of  his 
relations  with  respect  to  his  environment  and  with  respect  to  the  new 
element  which  is  supporting  his  weight,  the  air.  Either  instinctive 
action  or  carefully  considered  intentional  action  upon  the  part  of 
the  flier  is  determined  entirely  by  information  which  is  coming  into 
his  possession  concerning  his  relations  with  his  environment.  This 
information  can  be  had  by  him  only  through  the  activities  of  his 
special  senses.  But  possession  of  normal  perceptive  end-organs, 
nerve  paths,  and  brain  connections  does  not  constitute  definite  as- 
surance that  the  individual  will  accomplish  satisfactorily  balance 
or  orientation.  Further,  he  may  accomplish  balance  satisfactorily 
and  still  be  completely  disorientated;  or  he  may  be  properly  orien- 
tated and  fail  to  accomplish  balance  properly.  The  two  are  inde- 
pendent functions  of  the  mind,  closely  associated,  but  in  no  way 
functionally  interdependent.  On  the  other  hand,  lack  of  normal 
perceptive  apparatus  does  constitute  definite  assurance  that  the  in- 
dividual will  be  physically  less  able  to  accomplish  balance  or  orien- 
tation, or  both,  under  certain  circumstances  under  which  these  would 
be  possible  for  the  man  in  full  possession  of  normal  perceptive  appa- 
ratus. There  are  certain  circumstances  under  which  balancing  can 
be  performed  adequately  even  by  the  man  who  is  possessed  of  less 
than  full  normal  equipment.  There  is  no  doubt  that  man  can  ac- 
complish a  certain  kind  of  flying  blindfolded,  or  without  functionat- 
ing vestibular  apparatus,  or  without  normal  deep  sensibility.  Hence 
this  important  air  medical  problem  is  to  study  the  "peak  load" 
requirements,  the  conditions  of  emergency  and  confusion  which  may 
be  encountered  unexpectedly  in  the  air,  and  to  attempt  to  estimate 
carefully  the  minimum  perceptive  equipment  which  would  be  ade- 


112  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

quate  under  these  conditions  to  enable  the  flier  to  negotiate  such 
difficult  and  unusual  phases  of  flying.  There  are  certain  tempera- 
ments, certain  types  of  minds,  certain  intangibly  different  mental 
composites,  which  determine  the  inability  of  the  individual  to  nego- 
tiate these  critical  points  in  flying,  even  though  he  be  in  full  posses- 
sion of  his  sensory  perceptive  facilities.  "  Self  possession,"  "  cool- 
ness," "  bravery,"  "  sand,"  "  nerve,"  "  presence  of  mind,"  "  judg- 
ment," on  the  other  hand,  added  to  a  perceptive  equipment  of  less 
than  normal  may  determine  the  success  of  an  individual  in  emerging 
safely  from  a  critical  air  situation.  While  this  is  unquestionably 
the  fact,  these  mental  qualities  are  so  intangible,  so  indeterminable, 
and,  above  all,  so  distinctly  not  in  the  category  of  things  physically 
to  be  examined  and  measured  by  the  medical  examiner  that  it  is 
not  deemed  justifiable  for  the  physical  examiner  to  admit  into  the 
Air  Service  or  to  allow  to  remain  in  the  Air  Service  anyone  who  is 
discovered  to  be  lacking  in  acuity  prescribed  for  the  several  special 
senses  known  to  be  prime  requisites  of  the  flier. 

MOTION-SENSING   EXPERIMENTS   IN   LINEAR  UPWARD  AND  DOWNWARD  DI- 
RECTION.  GROUPS  TESTED. CONDITION    OF   TESTS. 

One  of  the  methods  of  approaching  the  problem  of  determining 
what  is  the  relative  value  of  the  various  sensory  contributions  to  the 
individual's  total  knowledge  concerning  motion,  was  a  series  of 
experiments  performed  in  a  bank  of  elevators  capable  of  performing 
vertically  upright  trips  40  stories  in  extent,  a  height  of  over  400  feet, 
at  a  maximum  speed  of  1,000  feet  per  minute.  For  this  purpose  four 
groups  of  individuals  were  selected,  namely,  (1)  normals,  (2)  deaf- 
mutes  totally  lacking  vestibular  perception,  (3)  deaf-mutes  pos- 
sessing vestibular  perceptions  in  various  degrees  below  the  normal, 
and  (4)  tabetics  whose  deep  sensibility  was  impaired  to  various  de- 
grees. These  experiments  were  carried  out  during  a  period  of  six 
weeks,  with  a  view  to  determining  the  average  ability  of  each  group 
to  sense  the  various  vertically  up  and  down  movements  to  which  they 
were  subjected.  The  elevator  shafts  were  entirely  dark,  and  the 
lights  on  the  cars  were  shut  off  during  the  experiments,  so  that  no 
information  reached  the  individual  via  the  visual  tract.  Each  indi- 
vidual of  the  normal  group  was  first  determined  to  be  possessed  of 
normal  vestibular  and  deep  sensibility. 

The  following  is  a  digest  of  the  findings : 

GROUP  1. 

FINDINGS  IN  NORMALS. 
ACCELERATION. 

1.  During  acceleration  upward  all  were  able  to  sense  accurately  the 
character  of  the  motion  to  which  they  were  subjected. 


MANUAL  OF  MEDICAL  BESEAECH   LABORATORY.  113 

SUSTAINED  SPEED. 

2.  A  slower  sustained  rate  of  speed  immediately  ensuing  upon 
acceleration  upward  was  uniformly  misinterpreted  as  arrest  of  mo- 
tion, or  as  very  slow  motion. 

RETARDATION. 

3.  Retardation  to  the  slowest  possible  continued  speed  upward, 
ensuing  upon  sustained  speed  upward,  was  universally  sensed  as 
motion  vertically  downward. 

GROUP  2. 
FINDINGS  IN  DEAD  VESTIBULE  DEAF-MUTES. 

4.  The  deaf  mutes  in  whom  the  vestibular  function  was  totally 
abrogated  sensed  acceleration  upward  correctly. 

5.  These  individuals  were  uniformly  inconsistent  in  describing 
the  character  of  slow  motion  vertically  upward  at  a  constant  rate  of 
speed,  sometimes  guessing  "  upward  "  and  sometimes  guessing  "  down- 
ward," but  always  acutely  sensitive  to  the  fact  that  they  were  under- 
going motion  of  some  kind. 

6.  Retardation,  ensuing  upon  motion  vertically  upward  at  a  sus- 
tained rate  of  speed,  was  uniformly  correctly  sensed  by  these  indi- 
viduals. 

7.  Arrest  of  motion  ensuing  upon  retardation  or  motion   at  a 
sustained  rate  of  speed  was  uniformly  correctly  sensed  by  these 
individuals. 

8.  In  these  individuals  it  was  impossible  to  produce  the  illusion 
of  reversal  of  motion  by  alteration  in  the  speed  of  the  car.    It  was 
apparent  that  absence  of  hearing  and  vestibular  sense  had  keyed 
up  to  a  high  degree  of  attention  and  sensitiveness  the  deep  sensi- 
bility tract,  though  it  is  not  believed  that  this  observation  justifies 
a  statement  that  the  sensing  of  the  deep  sensibility  impulses  was 
keener  than  that  of  the  normal  individual.    It  seems  certain,  how- 
ever, that  the  attentions  of  these  individuals  to  motion  perceptions 
coming  in  via  the  deep-sensibility  tract  were  more  intense  than  that 
of  the  ordinary  normal  individual. 

GROUP  3. 
FINDINGS  IN  LIVE  VESTIBULE  DEAF-MUTES. 

9.  Deaf-mutes  in  possession  of  intact  vestibular  apparatus  and 
normal  acuity  of  perception  absolutely  duplicated  the  findings  of 
the  first  group  of  full  normal  individuals  tested,  as  shown  in  items 
1,  2,  and  3  of  this  digest  of  results. 

8911&— 18 8 


114  MANUAL   OP   MEDICAL  RESEARCH   LABORATORY. 

10.  Deaf-mutes  in  whom  acuity  of  vestibular  perception  was  re- 
duced to  an  index  represented  by  two  or  three  seconds  duration  of 
nystagmus  and  no  past-pointing  and   almost   absent   falling  were 
able  to  sense  acceleration  vertically  upward  correctly  and  failed  to 
identify  slower  motion  at  a  sustained  rate  of  speed  upward,  but 
sensed  the  motion  very  positively,  though  labeling  it  at  times  "  mo- 
tion downward  "  and  at  other  times  "  motion  upward  "  ;  they  were 
able  to  detect  retardation  and  arrest  keenly,  but  did  not  experience 
the  illusion  of  reversal  of  motion  either  following  acceleration,  re- 
tardation, or  arrest  of  motion. 

GROUP  4. 
FINDINGS  IN  TABETICS. 

11.  Tabetics  in  whom  vestibular  tests  had  demonstrated  the  pres- 
ence of  normal  vestibular  functions  were  roughly  of  two  classes — 
the  lower  or  dorso-lumbo-sacral  type  and  the  higher  or  the  cervico- 
dorsal  type.     Both  types  evidenced  a  satisfactory  ability  to  sense 
acceleration  of  motion  vertically  upward;  slower  motion  at  a  sus- 
tained rate  of  speed  ensuing  upon  this  acceleration  upward  was  not 
sensed  at  all  by  either  type ;  retardation  following  motion  vertically 
upward  at  a  sustained  rate  of  speed  was  sensed  as  motion  downward 
by  both  types.    Particularly  striking  was  the  continuation  over  long 
periods  of  time  of  the  sensing  of  motion  downward  by  the  first  type 
of  tabetics  when  arrest  of  motion  ensued  upon  retardation  vertically 
upward.    Several  of  these  cases  continued  to  indicate  motion  down- 
ward for  from  30  to  60  seconds  following  total  arrest  of  motion. 
This  was  not  the  case  with  the  second  type  of  tabetics,  several  of 
whom,  however,  did  indicate  sensation  of  motion  downward  for  a 
few  seconds  following  total  arrest  of  motion. 

DOWNWARD  MOTIONS. 

12.  Acceleration  of  motion  downward  from  the  fortieth  floor  was 
correctly  sensed  by  normals,  both  types  of  deaf-mutes,  and  both  types 
of  tabetics. 

13.  Slower  motion  downward  at  a  sustained  rate  of  speed  ensuing 
upon  rapid  acceleration  downward  was  sensed  by  the  normals  uni- 
versally, as  either  complete  cessation  of  motion  or  extremely  slow 
motion  in  a  downward  direction;  this  was  also  the  case  with  the 
second  group  of  deaf-mutes,  those  in  possession  of  vestibular  func- 
tions; the  first  groups  of  deaf-mutes  were  unable  to  sense  the  char- 
acter of  sustained  motion  downward  accurately,  but  more  frequently 
guessed  "  downwards  "  than  "  upwards  " ;  the  tabetic  of  either  type 
indicated  almost  invariably  arrest  of  motion. 


MANUAL  OP  MEDICAL  RESEARCH   LABOBATORY.  115 

14.  Retardation  downward  ensuing  upon  motion  at  sustained  rate 
of  speed  downward  was  sensed  as  arrest  of  motion  or  as  slow  motion 
upward  by  the  normal  group  and  by  the  deaf-mutes  in  possession  of 
vestibular  function  and  by  both  types  of  tabetics.    This  confusion  of 
sensing  between  arrest  or  slow  motion  upward  was  consistent  with  all 
members  of  these  groups,  but  individuals  in  each  group  varied  in 
their  answers,  one  individual  sometimes  indicating  arrest  and  at  other 
times  indicating  slow  motion  upward. 

15.  Arrest  of  motion  ensuing  upon  retardation  downward  was  uni- 
formly indicated  as  slow  motion  upward  by  the  group  of  normals; 
the  group  of  deaf-mutes  in  possession  of  vestibular  function  sensed 
this  as  slow  motion  upward  only  for  a  second  or  two  and  then  indi- 
cated properly  total  arrest  of  motion ;  the  group  of  deaf-mutes  totally 
lacking  vestibular  perception  uniformly  indicated  correct  perception 
of  arrest  of  motion  on  the  instant;  both  types  of  tabetics  indicated 
sensation  of  motion  vertically  upward,  and  this  sensation  continued 
for  a  much  longer  period  of  time  than  in  the  normal  group. 

The  conclusions  from  the  above-outlined  experiments  are  that 
(A)  the  normal  individual,  the  deaf-mute  whose  vestibular  function 
is  unimpaired,  and  the  tabetics  whose  vestibular  functions  are  unim- 
paired seem  to  be  almost  equally  sensitive  to  acceleration  either  up- 
ward or  downward;  (B)  during  slower  motion  at  a  sustained  rate  of 
speed  upward  or  downward  the  deaf-mute  whose  vestibular  function 
has  been  totally  abrogated  is  totally  unable  to  sense  accurately  the 
character  of  the  motion  to  which  he  is  subjected,  but  he  is  keenly 
sensible  of  being  subjected  to. some  kind  of  motion;  whether  this  is 
vertically  upward  or  vertically  downward  seems  to  be  pure  guess- 
work. The  other  individuals  tested  all  evidenced  sensory  illusion 
and  always  in  the  shape  of  a  relative  reversal  varying  in  degree  be- 
tween a  sense  of  partial  or  complete  arrest  of  motion  and  inception  of 
motion  in  the  opposite  direction.  This  latter  was  more  marked  in 
the  tabetic.  This  would  seem  to  indicate  that  in  general  the  quantita- 
tive perception  of  motion  at  a  sustained  rate  of  speed  lies  more  par- 
ticularly within  the  province  of  the  deep  sensibilities;  the  qualitative 
perception — that  is,  determination  of  the  exact  direction  of  the 
motion — lies  within  the  province  of  the  vestibular  component  in  the 
total  composite  of  motion-perceiving.  (C)  Susceptibility  to  illusion 
of  a  motion-perceiving  naturally  is  directly  proportionate  to  the  keen- 
ness of  the  ability  to  make  accurate  qualitative  perceptions ;  in  other 
words,  the  illusions  of  motion  in  the  absence  of  vision  are  largely,  if 
not  exclusively,  attributable  to  the  vestibular  apparatus. 

It  should  be  added  that  for  the  purpose  of  conducting  these  experi- 
ments especial  control  was  added  to  the  regular  control  of  these  ele- 
vators, and  by  means  of  this  the  accelerations,  retardations,  and  mo- 
tions at  sustained  rates  of  speed  were  accomplished  with  almost  com- 


116  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

plete  absence  of  jarring  or  friction.  The  use  of  magnetic  brake 
control  adjusted  to  extreme  nicety  and  the  elimination  of  all  loose 
connections  and  joints  eliminated  sound  almost  completely ;  the  visual 
element  of  motion-sensing  was  absolutely  eliminated  by  the  conduct- 
ing of  the  tests  in  perfect  darkness ;  tactile  impulses  were  almost  com- 
pletely eliminated  by  lining  the  entire  car  with  thick  blankets,  pro- 
tecting the  subjects  from  access  of  air  currents  to  the  skin  throughout 
the  experiments. 

EXPERIMENTAL  STUDIES  ON  "  THE  FEEL  OF  THE  AIRSHIP." 
DEAF-MUTES  AND  NOBMALS. 

A  physiologic  function  which  is  peculiarly  important  in  aviation 
as  contrasted  with  all  other  branches  of  the  service  is  that  of  equili- 
bration. Nothing  could  better  illustrate  this  peculiar  importance  of 
the  inner  ear  than  a  comparative  study  of  those  with  normal  inner 
ears  as  contrasted  with  those  of  destroyed  inner  ears — deaf-mutes. 
A  series  of  experiments  was  conducted  in  actual  flights.  Those  with 
normal  inner  ears,  when  blindfolded,  were  able  to  detect  motion 
changes  accurately  during  the  flight,  whereas  blindfolded  deaf-mutes 
with  destroyed  labyrinths  were  not. 

In  order  to  appreciate  the  part  that  the  ear  mechanism  plays  in 
aviation,  all  that  any  physician  need  do  is  to  take  a  flight  in  an 
aeroplane.  As  you  guide  an  aeroplane  in  a  straight  flight,  your 
incessant  effort  is  to  correct  minute  deviations  from  the  level  posi- 
tion ;  the  countless  and  continuous  changes  of  movement  in  all  direc- 
tions are  counteracted  by  tiny  movements  of  the  joy  stick.  In  your 
first  flights,  when  instructor  is  guiding  the  plane,  you  watch  the  joy 
stick  in  front  of  you  and  you  notice  that  it  is  moving,  ever  so  little, 
this  way  and  that,  in  response  to  stimuli  in  the  detection  of  changes 
of  position.  This  sense  of  the  "  detection  of  movement "  is  what  the 
experienced  aviator  calls  "  the  feel  of  the  airship  " ;  it  is  that  sense 
which  distinguishes  the  born  flier  from  the  mechanical  flier,  who  is 
forced  to  rely  upon  his  sight  in  the  guiding  of  the  plane.  The 
Almighty  gave  certain  sense  organs  to  man;  if  there  is  any  indi- 
vidual who  preeminently  needs  a  normal  sensing  of  movement,  it  is 
obviously  the  aviator.  The  turning-chair  and  douching  tests  enable 
us  to  determine  whether  the  internal  ears  and  all  the  intracranial 
pathways  from  the  internal  ears  are  functioning  normally. 

WHAT  IS  "  FEEL.  OF  THE  AIRSHIP  "? 

One  of  the  terms  most  commonly  used  in  aviation  is  "  the  feel  of 
the  airship."  It  had  its  origin  at  the  beginning  of  aviation  and  seems 
to  be  a  phrase  which  in  the  mind  of  the  practical  flier  covers  every- 
thing which  goes  to  express  a  trained  aviator's  skill  in  the  proper 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  117 

and  semiautomatic  control  and  balance  of  an  airship.  Some  men 
give  evidence  of  possessing  this  sense-complex  during  the  first  one 
or  two  hours  of  instructions ;  others  never  acquire  it,  and  still  others 
show  it  in  such  a  moderate  degree  that  they  are  always  looked  upon 
with  apprehension  by  instructors,  who  feel  that  such  men  are  not  to 
be  depended  upon  in  an  emergency. 

Very  few  trained  pilots  can  give  any  clear  explanation  of  what  is 
meant  by  the  term,  except  to  say  that  if  the  beginner  does  not  possess 
it  he  will  never  be  able  to  make  a  first-class  pilot.  Some  explain  it 
by  a  keen  sense  of  motion ;  some  by  general  physical  dexterity,  some 
by  a  keen  sense  of  vision,  and  some  would  seem  to  credit  it  to  an 
inborn  special  sense  of  some  kind.  That  some  such  sense  or  com- 
bination of  senses  exists,  there  can  be  no  question.  This  general  fact 
has  been  appreciated  by  scientific  men  from  the  start,  and  much  of 
the  work  of  the  Medical  Eesearch  Laboratory  has  been  directed, 
consciously  or  unconsciously,  toward  scientific  explanation  of  this 
sense-complex. 

Evidently  motion-sensing  must  be  intimately  related  with  this 
proper  "  feel  of  the  airship."  As  previously  stated,  motion-sense  is 
dependent  upon  information  derived  from  (1)  muscle  sense,  (2) 
sight,  (3)  vestibular  sense,  and  (4)  tactile  sense. 

OBSERVATIONS    UPON    MOTION-SENSING    DURING    AIRPLANE    FLIGHTS. 
DEEP  MTJSCULAB  SENSIBILITY  STUDIED  BY  ELIMINATION. 

The  purpose  of  this  study  was  to  try,  by  elimination  of  any  two 
of  the  first  three  factors,  to  estimate  the  value  of  the  third.  The 
fourth,  tactile,  may  be  ignored,  being  constant  in  all  cases.  This  can 
be  done  as  follows:  Blindfolding  eliminates  sight;  the  use  of  deaf- 
mutes  with  destroyed  vestibular  apparatus  eliminates  the  vestibular 
sense;  blindfolding  these  deaf-mutes  eliminates  sight  and  vestibular 
sense,  leaving  the  deep  sensibility  as  the  remaining  factor.  Experi- 
mental study  with  cases  of  tabes  and  other  similar  cases,  where  the' 
deep  sensibility  is  involved,  are  now  being  carried  on  and  will  give 
us  further  data  on  deep  sensibility. 

TILTING  PEECEFTION. 

It  has  been  shown  by  various  observers,  experimenting  upon  thou- 
sands of  aviation  applicants,  that  there  exists  a  very  clear  appre- 
ciation of  tilting.  If  a  chair,  balanced  on  one  point,  is  so  slowly 
tilted  that  a  man  seated  in  it  can  not  sense  the  motion,  there  comes 
a  time  when  he  appreciates  that  he  is  tilted.  Laboratory  experiments 
of  this  sort  have  been  repeated  in  the  air  under  practical  flying 
conditions.  At  first  glance  it  would  seem  that  the  experimental 
errors  in  such  a  study  would  be  overwhelming,  but  a  more  extended 


118  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

investigation  in  the  plane,  at  various  altitudes  and  under  various 
weather  conditions,  corrects  this  impression  to  the  extent  that  for 
a  practical  study  of  the  "  feel  of  the  airship,"  theoretical  experimental 
errors  can  be  disregarded. 

POINTS  IN  EXPERIMENTS  TO  BE  NOTED. 

In  order  to  get  at  normal  responses  under  actual  air  conditions, 
five  points  must  be  observed:  (1)  Subjects  with  previous  flying  ex- 
perience must  be  eliminated ;  (2)  normal  individuals  must  be  selected, 
who  are  not  alarmed  by  the  thought  of  a  first  flight,  and  who  have 
trained  powers  of  observation;  (3)  a  professional  pilot  of  years  of 
flying  practice  must  be  used  whose  experience  would  enable  him  to 
appreciate  the  problems  and  hold  ,the  ship  at  the  given  angles  with 
the  greatest  degree  of  accuracy  in  spite  of  unfavorable  atmospheric 
conditions,  and  a  clinometer  used  by  him  to  measure  angles  of  tilt; 

(4)  the  same  plane  must  be  used  throughout  the  experiments;  and 

(5)  the  intercommunicating  phone  sys!o;u  must  be  used  between 
pilot  and  subject. 

KIND  OF  SUBJECTS   SELECTED.   • 

For  purposes  of  study,  15  candidates  were  selected  from  the  Sur- 
geons in  the  Medical  Research  Laboratory.  Chart  I  is  a  graphic 
diagram  of  the  results  of  the  experiments  on  normal  individuals 
who  have  never  had  any  previous  experience  in  the  air.  The  sub- 
jects were  blindfolded,  were  then  taken  up  in  the  plane,  and  the 
nianeuvers  indicated  were  carried  out.  The  lower  blue  line  shows 
/rne  movements  actually  executed  by  the  plane.  The  upper  red 
broken  line  shows  the  movements  the  subject  felt  were  being  executed. 

EXPLANATION  OF  CHARTS  I  AND  CHARTS  II  AND  III. 

There  is  a  very  important  difference  in  the  nature  of  carrying 
out  the  maneuvers  in  Chart  I  and  Charts  II  and  III.  In  the  first 
type  of  experiments,  conducted  in  Chart  I,  the  positions  were 
changed  by  markedly  quick  movements  of  the  plane,  i.  e.,  the  up- 
ward motion  was  the  sudden  zoom  upward,  the  downward  motion 
was  a  quick  almost  vertical  dive  downward,  the  banks  to  the  right 
and  left  were  done  quickly,  and  the  turns  on  the  horizontal  plane 
were  made  as  sharp  as  possible. 

If  a  quick  zoom  is  made,  the  feeling  is  that  you  are  being  thrown 
against  the  seat  by  centrifugal  force  and  in  a  quick  steep  bank  a 
similar  sensation  is  noticed.  In  the  start  of  the  nose  dive  one  is 
thrown  against  the  belt  by  the  action  of  the  centrifugal  force,  and 
it  is  not  a  matter  of  wonder  when  the  candidate  interchanges  in  his 
mind  movements  in  which  the  most  prominent  element  is  the  cen- 
trifugal action  forcing  his  body  against  seat  or  belt.  We  also  found 


Chart  1  represents  the  curves  of  normal  in- 
dividuals during  their  first  flights.  The 
blue  line  represents  evolutions  actually 
performed  by  the  machine,  the  red  line 
the  evolutions  the  subject  thought  were 
being  carried  out.  Where  the  line  is 
broken,  the  subject  had  no  idea  of  what 
was  going  on. 


NOTE. — Upper  line  on   the  original   chart  is  red, 
lower    line    is    blue. 


118-1 


118-2 


118-3 


D 


Chart  2  is  divided  into  two  parts,  A  and  B. 

Chart  2A  represents  the  subjects'  appreciation 
of  the  smallest  angle  in  a  downward  or  up- 
ward direction. 

Chart  2B  represents  the  subjects'  appreciation 
of  the  smallest  angle  in  a  bank. 

stalling  angle  of  the  machine,  past  which 
it  is  unable  to  execute  these  evolutions  is 
70  degrees  up.  40  degrees  down.  85  degrees 
on  the  banks. 


119-1 


RT 

£ka<4  a. 


119-2 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  119 

that  if  the  right  and  left  turns  were  kept  in  a  true  horizontal  plane 
without  banking,  that  it  is  very  difficult  to  differentiate  between  the 
two  on  account  of  the  large  size  of  the  circle  it  was  necessary  to 
describe  in  making  these  turns  without  side-slip.  A  short  analysis 
of  the  different  observation  flights  seem  to  show  that  the  general 
powers  of  observation  are  not  improved  during  an  individual's  first 
flights.  In  fact,  they  are  frequently  impaired  on  account  of  excite- 
ment and  apprehension,  and  a  short  analysis  of  the  personalities  of 
these  subjects  tends  to  explain  many  of  the  errors. 


CASE  HISTORIES. 


Case  I,  experiments  1  and  2,  Chart  I. — Young  man,  not  acute  ob- 
server, though  not  particularly  nervous.  Made  one  fundamental 
'error  on  first  flight  and  failed  to  sense  banks  or  slow  horizontal  turns. 
On  second  flight  he  made  no  fundamental  errors,  simply  mistaking 
right  and  left  horizontal  slow  turns. 

Case  II,  experiments  3  and  4,  Chart  I. — A  middle-aged  man,  badly 
scared  on  first  flight  and  was  all  at  sea.  On  second  flight  was  calmer 
and  made  no  fundamental  errors,  confusing  right  and  left  slow  hori- 
zontal turns  only. 

Case  III,  experiments  5  and  6,  Chart  I. — A  cool  phlegmatic  indi- 
vidual. He  mistook  turns  for  banks  during  the  first  flight,  but  made 
no  errors  on  his  second  flight. 

Case.  IV,  experiments  7  and  8,  Chart  I. — A  nervous  individual.  Did 
fairly  well  on  his  first  flight  and  improved  markedly  on  his  second, 
making  no  errors. 

Case  V,  experiments  9  and  10  and  11,  Chart  7. — A  young  man,  not 
particularly  a  good  observer  and  very  nervous  over  his  flight.  He 
got  very  little  correct  in  his  first  experiment  (9),  appreciating  cor- 
rectly only  horizontal  flight,  marked  upward  and  downward  move- 
ments, and  entirely  missed  right  and  left  horizontal  turns  and  right 
and  left  acute  banks.  His  second  flight  showed  considerable  improve- 
ment, appreciating  correctly  four  out  of  seven  manetfvers,  as  against 
three  in  the  first  flight,  but  far  less  than  the  others.  In  his  third  ex- 
periment (experiment  13)  he  made  only  one  bad  mistake  in  appre- 
ciating seven  maneuvers. 

Case  VI,  experiments  12  and  13,  Chart  I. — This  man  has  an  un- 
usual mentality ;  he  is  noted  for  his  muscular  dexterity,  is  an  amateur 
sleight-of-hand  performer  and  a  close  observer  under  all  conditions. 
He  made  no  mistakes  in  either  flight. 

Case  VII,  experiment  14,  Chart  I. — A  highly  trained  clinical  ob- 
server, has  an  extremely  keen  mind,  adventurous  in  spirit,  and  has 
large  experience  in  mountain  climbing  and  in  laboratory  work  at 
high  altitudes.  He  made  no  mistakes. 


120  MANUAL  OF   MEDICAL  EESEAECH   LABOBATOBY. 

Case  VIII,  experiments  15  and  16,  Chart  I. — A  fair  observer  only. 
In  his  first  flight  he  did  not  try  to  guess  as  many  of  the  more  nervous 
ones  did,  therefore  the  dotted  line.  The  second  flight  showed  im- 
provement, making  only  one  fundamental  error. 

Case  IX,  experiments  17  and  18. — A  man  over  50  years  of  age,  was 
very  nervous  about  his  first  flight,  but  improved  somewhat  during  the 
second,  still  making  several  fundamental  errors. 

Case  X,  experiments  19  and  W,  Chart  I. — A  trained  physiologic 
observer,  cool  and  calm,  and  made  no  mistakes  of  any  kind. 

Case  XI,  experiment  21,  Chart  I. — Highly  strung  young  man,  very 
tense ;  made  only  one  error  on  his  only  flight. 

EXPLANATIONS  OF  CHART  II,  III,   AND  IV. 

Charts  II,  III,  and  IV  represent  a  study  of  the  ability  to  detect 
gradual  departures  from  the  horizontal  flying  line.  In  contradis- 
tinction to  the  first  series  of  observations  the  endeavor  here  was  to 
make  the  change  in  the  angles  so  gradual  that  the  candidate  would 
appreciate  his  change  from  the  horizonta  i  in  addition  to  sensing  the 
forward  movement  of  the  plane.  The  endeavor  was  to  eliminate 
suddenness  in  change  of  direction  as  much  as  possible.  They  were 
conducted  with  the  greatest  care  and  only  during  ideal  weather. 
The  angles  were  checked  by  using  a  clinometer  and  every  effort 
possible  was  made  to  eliminate  experimental  error.  The  intercom- 
municating phone  system  was  used.  As  soon  as  a  proper  altitude 
was  reached,  where  the  air  was  smooth,  the  subject  blindfolded  him- 
self and  as  soon  as  he  was  able  to  appreciate  whether  he  was  going 
up  or  down,  or  banking  to  the  left  or  "to  the  right,  he  would  so  report 
to  the  pilot.  The  pilot  would  then  maneuver  the  plane  to  repeat  this 
angle  from  6  to  10  times  or  until  he  was  positive  of  the  smallest 
angle  that  the  subject  was  capable  of  'appreciating,  when  he  .would 
write  down  his  result.  The  remarkable  similarity  of  the  results  is 
in  itself  proof  that  the  experimental  errors  were  slight,  or  at  least 
were  about  equal  in  all  cases  and,  therefore,  to  be  neglected. 

CHABT    2-A. — OBSERVATIONS    UPON    MOTION-SENSING    DURING    AIRPLANE    FLIGHTS. 

In  this  series  of  experiments  some  of  the  subjects  had  never  flown, 
while  others  had  had  a  few  flights  previously  in  the  other  series  of 
experiments.  It  is  to  be  noted  that  in  this  series  the  downward  angle 
was  detected  in  every  case  more  accurately  than  the  upward  angle; 
the  upward  angle  was  less  accurately  detected  by  men  making  their 
first  flight.  One  of  these  beginners  was  unable  to  detect  the  upward 
angle  even  to  70  degrees,  the  stalling  angle  of  the  machine.  Subse- 
quent examination  showed  that  this  man's  vestibular  reactions  were 
very  much  subnormal,  as  evidenced  by  10  seconds'  duration  of  nystag- 


w.  |.  W.II.'U 
(   -a  y-  i« 
f— •<   ''• 

iK'l    Uoc^if 


Chart  3  illustrates  the  appreciation  of  angles 
by   professional   fliers. 


120 


Chart  4  represents  experience  of  deaf-mutes  similar 
to  experiments  shown  in  chart  1.  The  blue  or 
lower  line  represents  evolutions  actually  performed 
by  the  machine.  The  red  or  upper  line  represents 
the  evolutions  the  subject  thought  were  being  car- 
ried out.  Where  the  line  is  broken  the  deaf-mute 
had  no  idea  what  was  being  carried  out. 


121-1 


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MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  121 

mus,  no  past-pointing,  and  only  very  slight  tendency  to  fall.  The 
general  average  of  these  upward  and  downward  experiments  show 
upward  angle,  17  degrees ;  downward  angle,  9  degrees. 

CHABT   2-B. 

Chart  2-B  represents  a  series  of  experiments  similar  to  those  just 
described,  except  that  the  angles  were  banking  (lateral)  angles 
instead  of  upward  and  downward  (forward)  angles.  This  series  of 
experiments  showed  a  similarity  in  the  ability  to  detect  lateral 
changes  from  the*  horizontal.  A  curious  development  was  that  in 
this  series  the  banks  to  the  left  were  more  accurately  detected  by 
the  subjects  than  similar  banks  to  the  right. 


CHAET  4. 


Chart  4  shows  the  most  interesting  results  of  all.  Seven  deaf- 
mutes  were  the  subjects  of  these  experiments.  Two  showed  normal 
vestibular  function,  four  showed  absolute  lack  of  vestibular  func- 
tion, and  one  showed  a  very  small  amount  of  vestibular  function 
as  represented  by  three  seconds  of  nystagmus.  The  results  of  these 
experiments  upon  deaf-mutes  are  further  divided  into  three  groups. 
The  findings  of  the  first  groups,  those  with  absolutely  no  vestibu- 
lar function,  showed  total  inability  to  detect  changes  in  the  series 
of  movements  of  the  plane  in  any  of  the  six  flights  per  individual. 
The  results  of  experiments  with  the  second  type  of  deaf-mutes,  in 
which  only  a  vestige  of  vestibular  function  remained,  are  almost 
identical  with  those  of  the  first  group.  The  third  type  of  deaf- 
mutes,  in  full  possession  of  vestibular  function,  showed,  however,  a 
marked  improvement  over  the  others  in  successive  flights,  and  prac- 
tically the  normal  index  as  to  accuracy  of  detection  of  the  move- 
ments of  the  plane  in  the  later  flights. 

CHAET  m. 

Chart  III  consists  of  a  series  of  observations  carried  out  under 
the  same  conditions  upon  three  professional  fliers  and  one  profes- 
sional trick  motor-cyclist.  Their  superiority  in  detecting  angles  is 
at  once  apparent.  Still  more  interesting  is  the  fact  that  the  motor- 
cyclist, who  had  practically  no  flying  experience,  did  not  detect 
angles  as  well  as  the  pilots,  but  still  appreciated  them  better  than 
did  other  subjects  inexperienced  in  balancing. 

Other  experiments  with  other  normals,  not  noted  on  these  charts, 
convinced  us  that  the  results  so  far  given  represent  very  accu- 
rately the  general  average  in  such  individuals,  and,  therefore,  ex- 
periments of  a  greater  number  were  not  considered  necessary  for 
this  preliminary  study. 


122  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


DEAF-MUTE  EXPERIMENTS. 
CHABT  IV. 


Chart  IV  is,  as  has  been  said,  the  most  interesting  of  all.  Seven 
deaf-mutes  were  selected  whose  labyrinth  findings  are  given  on  the 
edges  of  the  charts.  The  striking  differences  between  these  deaf- 
mutes  and  the  normal  candidates  and  the  still  more  striking  lack 
of  improvement  in  all  their  subsequent  flights  seem  to  be  fairly  con- 
vincing that  for  purposes  of  appreciating  changes  of  position  in 
space  a  properly  functionating  vestibular  apparatus  is  of  great  im- 
portance, and  further,  but  little  can  be  expected  from  deep  sensibil- 
ity when  it  alone  senses  motion.  These  deaf-mutes  were  all  highly 
interested  and  were  keenly  alive  to  the  experiments.  Some  of  them 
were  convinced  that  they  would  prove  able  to  qualify  for  aviation, 
and  when  their  charts  were  shown  to  them  their  amazement  was  ex- 
treme. Their  guesses  as  to  the  kind  of  motion  to  which  they  had 
been  subjected  were  of  the  wildest  character.  They  had  nothing 
to  inform  them  except  their  deep  sensibility  and  tactile  sense.  Nose 
dives  and  the  "  zoom  "  or  upward  movements  were  carried  out  at 
such  acute  angles  that  it  was  remarkable  that  they  guessed  as 
inaccurately  as  they  did.  On  close  questioning  many  of  them  ad- 
mitted that  they  were  entirely  "  in  the  dark "  and  felt  as  if  they 
must  tear  the  bandage  from  their  eyes;  in  other  words,  they  were 
completely  lost  in  space,  and  it  is  greatly  to  their  credit  that  they 
were  willing  to  subject  themselves  repeatedly  to  these  more  or  less 
trying  experiences. 

One  of  the  most  important  observations  of  all  is  seen  in  an  ex- 
amination of  Chart  V.  As  a  matter  of  interest,  before  these  subjects 
were  sent  up,  we  tried  them  walking  a  straight  line  blindfolded, 
which  they  did  in  a  fairly  accurate  manner,  but  when  they  were 
asked  to  maintain  themselves  in  equilibrium  by  standing  on  one  leg 
with  eyes  closed,  they  fell  in  various  directions  and  none  of  tfyem 
were  able  to  stand  at  all  steadily  in  this  position.  After  rapid  rota- 
tion with  the  head  forward  and  eyes  closed,  they  were  quite  as  able 
to  stand  as  they  had  been  before,  showing  no  tendency  toward  the 
normal  falling  response.  They  were  dependent  for  sensory  informa- 
tion in  walking  or  standing  on  one  leg,  etc.,  upon  only  two  sources — 
vision  and  deep  sensibility. 

In  the  angle  experiment,  shown  on  Chart  V,  where  rapid  accelera- 
tion of  motion  was  made,  not  a  single  subject  was  able  to  guess  a 
single  correct  position  in  space.  The  machine  was  brought  up  to  the 
stalling  angle  above,  to  the  extreme  diving  angle  below,  and  to  such 
an  acute  bank  that  the  vertical  control  became  the  rudder,  and  because 
the  change  was  gradually  brought  about,  they  were  still  unable  to 
appreciate  any  deviation  from  the  horizontal.  This  preliminary 


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Chart  5  represents  for  deaf-mutes  what  chart 

2    represents   for   normals. 

Chart   5A   represents    the   subjects'    apprecia- 

tion of  the  smallest  angle  in  downward  or 

upward   direction. 

Chart  2B  represents  the  subjects  appreciation 

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of  the  smallest  angle  in  bank. 

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The  stalling  angle  of  the  machine,  past  which      ' 

it   is   unable  to   execute   these  evolutions   is 

70  degrees  up,  40  degrees  down,  25  degrees      >  .. 

on   the   banks. 

It  is  to  be  noted  that  in  no  case  was  the  deaf- 

mute  able  to  appreciate  any  of  these  angles. 

Therefore,  all  of  the  lines  are  broken. 

122-1 


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MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  123 

study  was  made  in  the  hope  that  the  peculiar  impression  which  has 
gone  abroad  and  which  has  done  much  to  block  the  progress  of  the 
selection  of  aviation  candidates — that  the  less  acute  motion-sense  of 
the  inner  ear  was  the  less  dizzy,  and  therefore  the  better  flier  the 
man  would  make,  would  be  corrected. 

The  findings  (covering  seven  days  of  experimental  work,  including 
52  flights)  as  to  the  motion-sensing  of  the  two  deaf-mutes  with  nor- 
mal vestibular  reactions  give  undoubted  evidence  of  gradual  improve- 
ment in  correct  sensing  of  motion ;  one  deaf-mute  with  a  vestige  of 
vestibular  function  shows  some  improvement  in  ability  to  sense  mo- 
tion correctly;  four  deaf-mutes  with  no  vestibular  function  show  no 
evidence  of  improvement  in  motion-sensing  ability.  It  must  be  borne 
in  mind  that  such  a  series  of  experiments  should  be  much  greater  and 
should  cover  a  much  longer  period  of  time  if  deductions  of  a  final 
nature  are  to  be  drawn.  The  injection  of  so  many  extraneous  influ- 
ences, such  as  apprehension,  fear,  excitement,  inability  to  focus  at- 
tention, vitiates  to  a  considerable  extent  the  value  of  the  findings  in 
any  individual  flight.  On  the  other  hand,  guesswork  injects  an  ad- 
ditional element  of  unreliability  into  the  findings.  While  analysis 
of  the  charted  records  shows  some  surprising  inconsistencies,  it  is  at 
once  apparent  that  normals  show  no  such  diametrically  opposite 
consecutive  motion-sensing  perceptions  as  the  deaf-mutes.  It  is  dem- 
onstrated by  this  series  of  experiments  that  man's  ability  to  sense 
motion  is  measured  by  his  full  possession  of  visual  acuity,  deep  sensi- 
bility, vestibular  sense  acuity,  and  tactile  sense.  And  particularly, 
that  the  "  feel  of  the  airship  "  which  *is  the  sense-complex  that  makes 
for  a  first-class  pilot,  requires  normal  vestibular  motion-sensing. 

4.  EXPERIENCE  AND  EDUCATION  IN  MOTION-SENSING  AND  FATIGUE  or 
THE  VESTIBULAR  END-ORGANS. 

The  possibilities  of  a  person  accustoming  or  educating  himself  by 
constant  rotation  to  estimate  correctly  the  sensations  of  vertigo  or 
disturbed  relations  in  space  have  been  considered,  and  experiments 
were  carried  out  with  a  view  to  shedding  light  upon  this  question. 
The  matter  is  one  of  practical  importance,  and  upon  it  the  life  of  an 
aviator  may  depend  in  a  critical  moment.  Adjustment  in  seasick- 
ness, in  whirling  dances,  in  acrobatics,  and  in  any  other  line  of  work 
where  rapid  changes  of  spacial  relations  are  necessary  has  long  been 
known.  It  has  been  a  disputed  point  as  to  whether  the  duration  of 
the  nystagmus  in  such  cases  actually  becomes  less  and  less  with 
the  same  stimulus.  By  experiment  it  was  found  that  nystagmus 
occurs  less  in  duration  after  repeated  turnings,  and  the  sensation 
of  vertigo  becomes  less  intense.  The  immediate  shortening  of  dura- 
tion of  nystagmus  and  the  lessening  of  vertigo  in  whirling  dancers 
or  others  ensuing  upon  excessive  stimulation  of  the  vestibular  end- 


124 


MANUAL   OP   MEDICAL  RESEARCH   LABORATORY. 


organs  is  a  transitory  fatigue  phenomenon.  The  average  normal, 
whose  nystagmus  time  when  not  fatigued  is  approximately  24  to 
26  seconds,  is  the  man  who  is  physically  most  suitable  for  flying 
training.  Many  experiments  concerning  acute  and  chronic  fatigue 
phenomena  are  now  under  consideration  in  this  laboratory  and  will 
be  reported  upon  later.  (See  Editorial  Insert,  p.  193.} 

The  whirling  artists,  who  spend  years  in  professional  whirling 
acts,  when  not  fatigued  show  full  normal  responses  to  tests  of  their 
vestibular  apparatus.  Their  art  lies  in  the  education  and  experience 
which  they  have  gained  and  in  the  dexterity  they  have  acquired  in 
the  repeated  performance  of  their  acts.  For  instance,  a  whirling 
dance  may  be  creditably  performed  by  a  novice,  but  the  professional 
whirling  dancer  will  demonstrate  his  ability  to  stop  dead  still  sud- 
denly without  a  fall,  whereas  the  novice  will  fall,  because  of  the 
vertigo  (or  false  sense  of  motion)  he  experiences  as  a  result  of  his 
whirling.  The  difference  between  the  artist  and  the  novice  lies  in 
the  artist's  ability  to  place  proper  construction  upon  his  false  sense 
of  motion,  experience  and  education  enabling  him  to  estimate  its 
degree  of  falsity  so  correctly  that  he  is  able  to  calculate  his  voluntary 
muscular  control  in  a  manner  that  results  in  his  accomplishing  a 
successful  standing  still.  The  novice,  unpracticed  and  inexperienced 
in  estimating  vertigo,  finds  himself  unable  to  do  so  successfully  and 
falls  to  the  floor. 

TESTS  OF  WHIRLING  ARTISTS,  DANCERS,  AND  EQUILIBRISTS,  FEB.   28,  1918. 


"L.  L."  whirling  artist. 
Nyst.  R.  26  sec.,  L.  24  sec. 

P.P.. 


FallB. 


rp    -p   /R.  hand  5. 
'  K'  \L.  hand  4. 

T     f  R.  hand  3. 

**  \L.  hand  3. 
fR.  normal. 
\L.  normal. 


"J.S.,"  equilibrist. 
Nyst.  R.  26  sec.,  L.  24  sec. 


P.P. 


R.  hand  3. 
L.  hand  1. 
n,  T  /R.  hand  1. 
To  L'  \L.  hand  3. 
fR.  normal. 
\L.  normal. 


" I.  B.,"  tight  and  slack  wire  artist. 
Nyst.  R.  28  sec.,  L.  33  sec. 

P.P.. 


fm 
To 


JR.  hand  2. 
'J  \L.  hand  2. 

/R.  hand  2. 
•  \L.  hand  2. 
R.  nornial. 


/R. 
•\L. 


normal. 


"C.  G.,"  balance  equilibrist. 
Nyst.  R.  25  sec.,  L.  20  sec. 


P.  P. 


Falls. 


R.  hand  3. 
L.  hand  2. 
JR.  hand  2. 
•  \L.  hand  3. 
R.  normal, 
normal. 


.ToL 

/R. 
•\L. 

Jfw/"JB.  B.,"  whirling  artist. 
Nyst.  R.  34  sec.,  L.  35  sec. 


P.P. 


ToT? 
To  R- 


:.  hand  3. 
[L.  hand  3. 
|TnT    /R.  hand  3. 
^To  L'  \L.  hand  3. 
rviio  /R-  normal. 

Falls JL.  normal. 


"C.  F.,"  whirling  dancer. 
.Nyst.  R.  29  sec.,  L.  31  sec. 

P.  P.. 


15 

R" 


Falls. 


R.  hand  1. 

L.  hand  1. 
m    T    JR.  hand  2. 
olj-  \L.  hand  2. 
fR.  normal. 
\L.  normal. 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 
"6.,"  whirling  dancer. 


125 


Nyst.  R.  27  sec.,  L.  28  sec. 
P.  P 

Falls 

"P.  A.,"  perch  act,  20  years  old,  13  years 
experience. 

Nyst.  R.  31  sec.,  L.  38  sec. 


,T_  p  /R.  hand  3. 
JiolML.  hand  3. 

P.P  

]TnT  JR.  hand  1. 
LioJj-  \L.  handl. 
fR.  normal. 

Falls  

\L.  normal. 

hand  2. 
hand  1. 

m    T     fR.  hand  5. 
•°  L-  \L.  hand  6. 


fTo  R.  {R- 
P.P 

™« v-fe'JSg: 

"  Mrs.  S.,"  whirling  act. 
Nyst.  R.  31  sec.,  L.  25  sec. 


P.  p  

CT>^  Tf  /R-  hand  3. 
|To  R"  \L.  hand  3. 

P.  P  

Falls  

IT,  T  /R.  hand  3. 
110  L'  \L.  hand  3. 
JR.  normal. 

Falls  

\L.  normal. 

"E.  M.,"  head  balancer,  41  years  old,  20 
years'  experience. 

Nyst.  R.  34  sec.,  L.  31  sec. 

P    fR.  hand  3. 
*"  {L.  hand  2. 
T     fR.  hand  3. 
**  \L.  hand  4. 
fR.  normal. 
\L.  normal. 

"C.  A.,"  perch  act,  28  years  old,  13  years 
experience. 

Nyst.  R.  21  sec.,  L.  24  sec. 


P.  P. 


TP  i,  fR.  normal. 

Falls \L.  normal. 

"Mrs.  H.,"  whirling  act. 
Nyst.  R.  22  sec.,  L.  24  sec. 

I 


R.  hand  1. 
L.  hand  1. 
R.  hand  2. 
.  hand  3. 


2. 
L.  hand  2. 


|Tn  T    /R.  hand  1. 
110  L'  \L. 


fR.  normal. 


hand  1. 


CONVERSATION  WITH  "  G  "  AND  "  B 


fR. 

\L.  normal. 

PROFESSIONAL  BALLET  DANCERS. 


"  Very  little  dizziness  even  when  learning,  but  individual  varia- 
tion; conquest  of  dizziness  depends  upon  acquisition  of  ability  to 
jerk  head  as  dancer  revolves.  Revolving  with  head  not  jerking, 
eyes  open  or  shut,  causes  dizziness.  Refused  to  revolve  jerking  head 
with  eyes  shut,  because  it  would  be  sure  to  cause  dizziness  and 
nausea ;  they  were  sure  it  was  much  worse." 


"Mrs.  S.,"  aerial  flying  trapeze,  SO  years 


P.  P. 


hand  3. 

hand  2. 
fR.  hand  2. 

hand  3. 
normal, 
normal. 


9  years  experience. 
Nyst.  R.  37  sec.,  L.  30  sec. 


P.  P 


old,  SO  years  in  circus. 
Nyst.  R.  17  sec.,  L.  18  sec. 

If  on.  {I 
ITO  L.  £ 

f  T? 

•{L: 

Cases  "A"  and  "  B  "  were  tight-rope  walkers. 


"L.  M.,"  head  balancer,  18  years  old,  8  or 


R.  normal, 
normal. 


-  hand  3. 
hand  2. 

-  hand  2. 
L.  hand  4. 


"A." 

Nyst.  R.  26  sec.,  L.  26  sec. 

fTo  R.  (R- 
**" 

ToL. 


P.P. 
Falla. 


fR. 
•\L. 


hand  3. 
hand  3. 
.  hand  3. 
.  hand  3. 
normal, 
normal. 


"B. 


Nyst.  R.  26  sec.,  L.  26  sec. 

[To 
P.  P 


-  hand  3. 
L.  hand  3. 


T_  T    fR.  hand  3. 
0  L-  \L.  hand  3. 
Falls  /R-  normal. 

*allfl \L.  normal.   . 


126 


MANUAL  OF   MEDICAL  RESEAKCH   LABOKATOKY. 


Cases  "  C,"  "  D,"  «  E,"  and  "  F  " 
"C,"  26  years  old,  6  years'  experience. 

Nyst.  R.  22  sec.,  L.  24  sec. 

Tn  P   JR-  kand  3. 

p   P  I  i(  K<  \L.  hand  3. 

lT    JR.  hand  3. 
**•  \L.  hand  3. 
R.  normal. 
L.  normal. 


"E,"  26  years  old,  6  years'  experience. 
Nyst.  R.  26  sec.,  L.  26  sec. 

P.P... 


Falls. 


fR.  hand  3. 
•  \L.  hand  3. 

!TO  L  IR'  hand  3< 
J'  \L.  hand  3. 

fR.  normal. 
\L.  normal. 


were  motordrome  whirling  racers 
"D"  23  years  old,  5  years'  experience. 

Nyst.  R.  26  sec.,  L.  26  sec. 

|Tr>  ft   /R-  hand  3 
10  n-  \L.  hand  3 
TA  T    /R.  hand  3 
J'  \L.  hand  3 
Falls  /R'  normal- 

ialls \L.  normal. 

"F,"  24  years  old. 

Nyst.  R.  8  sec.,  L.  8  sec. 

fmrtp    fR.handT 

p  p  '  *"  \L.  hand  T 

'  r |Tn  T     fR.handT 

IT°  L"  \L.  hand  T 

F  n  /Falling  absent. 

*  aus \Falling  absent. 


Applicant  "  F  "  was  a  vigorous,  robust  young  man  and  from  all 
appearances  the  most  promising  applicant  of  the  day.  The  caloric 
test  was  given  68°  douche  in  both  right  and  left  ears  with  same  sub- 
normal reaction.  This  man  had  formerly  ridden  a  motorcycle  at 
the  rate  of  50  miles  per  hour  on  circular  wall  on  motordrome  and  had 
never  experienced  nausea  or  dizziness.  A  4-f-  Wasserman  and  his- 
tory of  recent  chancre  explained  the  reactions. 

Many  important  practical  applications  may  be  the  outcome  of  these 
experiments.  It  may  ultimately  become  a  routine  method  of  accus- 
toming the  young  pilot  to 'the  sensations  of  the  spinning  nose  dive 
and  the  rolling  motion  of  the  airship  by  revolving  exercises.  Most 
important  of  all  may  be  the  possibility  of  teaching  the  prospective 
flier  the  sensations  of  the  loop,  tight  spiral,  and  spinning  nose  dive 
and  how  to  control  himself  during  the  incidental  vertigo  by  daily 
practice  in  some  such  apparatus  as  that  devised  by  Ruggles. 

The  most  common  revolving  motions  of  the  aeroplane  are  the  spiral, 
spinning  nose  dive,  and  the  roll.  In  the  spinning  nose  dive,  or  tight 
spiral,  the  aviator  may  have  his  horizontal  canals  or  his  vertical 
canals  chiefly  affected  according  to  the  position  he  assumes.  Since 
every  individual  is  more  accustomed  to  the  horizontal  canal  stimula- 
tion than  the  vertical  canal  stimulation,  it  is  better  that  he  assume  a 
position  in  which  the  horizontal  canals  are  mainly  stimulated.  In 
spiral  turns,  if  the  aviator  sits  jipright,  the  horizontal  canals  are  the 
ones  mainly  stimulated,  and  these  very  slightly,  because  of  the  large 
circular  turns.  In  the  spinning  nose  dive  the  ship  noses  vertically 
down,  due  to  the  heavy  engine  and  if  the  aviator  remains  in  the  same 
upright  position  as  in  horizontal  flying  he  will  then  concentrate 
stimulation  upon  his  vertical  canals.  But  if  he  bends  forward  as 
the  French  aviators  are  instructed  to  do,  he  will  practically  be  upside 
down  so  that  again  he  will  concentrate  stimulation  upon  the  horizon- 


MANUAL  OP   MEDICAL  RESEARCH   LABORATORY.  127 

tal  semicircular  canals.  Physical  directors  have  advised  turning 
movements  as  practice  exercises ;  but  after  all  this  is  only  of  prelimi- 
nary value,  because  experienced  fliers  become  so  accustomed  to  turn- 
ings and  air  antics  that  they,  like  acrobats,  know  where  they  are  at 
all  times  and  are  at  home  in  the  air. 

Space  does  not  permit  in  this  article  to  quote  from  the  histories 
of  aviators  at  the  disposal  of  the  otologic  department  cases  where,  fol- 
lowing impairment  of  the  labyrinth  due  to  mumps  or  syphilis,  a  man's 
flying  ability  has  been  lost  or  badly  impaired  coincidentally  with 
the  rapid  deterioration  of  his  vestibular  sensory  acuity.  This  is  ad- 
ditional corroborative  evidence  of  the  most  convincing  nature. 

RESUME. 

General  condition  of  aviator's  ears,  nose,  and  throat  must  be  good. 

The  ground  soldier  can  stand  still.  The  aviator  can  not.  Motion 
assumes  great  added  importance  to  the  aviator. 

Motion-sensing,  therefore,  assumes  great  additional  importance  to 
the  aviator. 

Of  the  senses  concerned  in  motion-sensing,  the  vestibular  sense  is 
the  only  one  whose  utility  remains  constant;  hence  the  necessity 
of  determining  the  aviator's  possession  of  requisite  vestibular  sense. 

Vestibular  tests  not  only  determine  functional  condition  of  this 
portion  of  the  internal  ear  but  give  definite  information  concerning 
the  integrity  of  parts  of  the  medulla  oblongata,  pons,  cerebrum,  and 
particularly  the  cerebellum. 

It  has  been  determined  that  up  to  18,000  feet  there  occurs  no 
marked  functional  change  in  the  vestibular  apparatus. 

Observations  made  in  an  extensive  series  of  blindfold  experiments 
on  normal  persons,  on  persons  with  nonf  unctionating  vestibular  appa- 
ratus, on  persons  lacking  hearing  only,  and  on  persons  with  impaired 
deep  sensibilities  indicate  that  perception  of  motion  in  a  linear 
direction — 

(a)  During  acceleration,  is  sensed  most  accurately  by  those  whose 
vestibular  apparatus  is  functionating; 

(&)  At  a  sustained  rate  of  speed  is  sensed  accurately  by  each 
group  except  those  lacking  deep  sensibility ; 

(c)  During  retardation  is  sensed  accurately  by  those  whose  vesti- 
bular apparatus  is  functionating ; 

(d)  Arrest  of  motion  ensuing  upon  motion  in  a  linear  direction 
is  most  accurately  detected  by  the  group  lacking  vestibular  function 
but  in  possession  of  unimpaired  deep  sensibilities. 

Experience  in  aeroplane  flights  shows  that  blindfolded  normal 
persons  perceive  motion  changes  accurately ;  that  blindfolded  persons 
lacking  normal  vestibular  apparatus  do  not. 


128  MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 

Transitory  fatigue  may  be  observed  after  excessive  stimulation  of 
the  vestibular  end-organs. 

Special  ability  to  estimate  correctly  the  degree  of  falsity  of  oft- 
repeated  motion-sensing  illusions  may  be  developed  in  normal  per- 
sons through  experience  and  education.  This  special  ability  enables 
its  possessor  to  maintain  safe  bodily  relation  with  his  environment 
during  the  existence  of  the  motion-sensing  illusions  with  which  he  has 
become  familiar  through  long  experience. 

A  superficial  observation  might  suggest  that  possibly  the  safest 
aviators  would  be  those  lacking  vestibular  function,  such  as  deaf 
mutes,  inasmuch  as  they  are  incapable  of  developing  motion-sensing 
illusions  which,  in  normal  persons,  ensue  upon  spinning  nose  dives  or 
other  whirling  aeroplane  maneuvers.  Possession  of  normal  function- 
ating sensory  end-organs  always'  entails  the  possibilities  of  subjec- 
tive sensory  illusions,  but  to  argue  the  advantage  of  lacking  such 
special  sense  end-organs  is  to  reach  the  reductio  ad  absurdum. 

One  who  shows  good  responses  in  the  turning-chair  shows  good 
detection  of  movement  in  the  air;  one  who  shows  poor  responses 
in  the  turning-chair  shows  poor  detection  of  movement  in  the  air. 
There  is  this  direct  relation  between  the  chair  and  the  air  and  the 
air  and  the  chair. 

THE  EAR  IN  STUNT  FLYING. 

Crashes  that  occur  during  "stunt"  flying  are  usually  the  result 
of  something  having  gone  wrong  with  the  pilot.  Hence  it  is  a  perti- 
nent matter  for  medical  investigation.  Just  what  this  something  is, 
is  not  always  clear.  Poor  judgment,  a  sense  of  bravado,  carelessness, 
"stunting"  at  low  altitudes,  and  sudden  faintness  are  among  the 
reasons  generally  offered  in  explanation  of  these  accidents.  Direct 
testimony  of  the  pilot  is  not  always  available,  since  many  of  the 
crashes  result  fatally.  Neither  are  pilots  who  have  crashed  and 
survived  always  able  to  give  a  clear  and  concise  account  or  analysis 
of  the  causes  of  the  accident. 

Underlying  them  all,  however,  there  runs  a  story  of  momentary 
loss  /of  faculties,  resulting  in  a  manipulation  of  controls  without 
deliberate  judgment.  Most  accounts  of  crashes  read,  "  The  pilot  went 
into  a  tail  spin  and  failed  to  come  out."  The  story  of  Lieut.  J.  M.  M. 
is  quite  typical  of  those  collected  by  this  department. 

While  flying  he  went  into  a  tail  spin.  This  produced  such  over- 
powering dizziness  that,  not  knowing  what  he  was  doing  or  why,  he 
grabbed  the  "  joy  stick  "  and  pushed  it  forcibly  over  and  threw  him- 
self into  another  tail  spin  in  the  opposite  direction.  Before  he  could 
come  out  of  this  he  crashed. 

So  many  of  the  accounts  of  crashes  given  by  pilots  who  did  survive 
emphasize  dizziness  (or  vertigo) ,  that  the  organ  responsible  for  dizzi- 


VI EW  OF  SEMICIRCULAR  CANALS  IN  BASE  OF  SKULL 


9 


fc 

* 


,-r 


SPINNING  NOSE  DIVE. 


MANUAL  OF  MEDICAL  RESEARCH   LABOBATOBY.  129 

ness  when  an  individual  is  whirled  around,  namely,  the  ear,  was  nec- 
essarily made  the  subject  of  investigation  by  the  Otologic  Depart- 
ment of  the  Medical  Research  Laboratory  at  Mineola,  N.  Y.  Experi- 
ments which  involved  the  whirling  of  individuals  point  conclusively 
to  the  fact  that  Stunt  Flying  is  essentially  an  Ear  Problem. 

By  visualizing  the  position  of  the  pilot  as  he  is  whirled  in  the 
various  stunt  evolutions,  it  was  found  that  by  reproducing  a  similar 
whirling  in  the  apparatus  it  was  possible  to  simulate  all  the  subjective 
effects  of  stunt  flying. 

Lieut.  J.  F.  D.  (150  hours  in  the  air)  was  placed  in  a  certain 
position  and  whirled.  He  volunteered  the  information  that  his 
sensations  were  identical  with  those  experienced  when  coming  out 
of  a  spinning  nose  dive.  When  placed  in  the  apparatus  in  a  certain 
different  position  and  whirled,  he  stated  that  his  sensations  were  those 
experienced  when  coming  out  of  a  tight  spiral.  Lieut.  W.  E.  R,.,  an 
experienced  pilot,  when  placed  in  the  same  position  as  Lieut.  D.'s 
first  position  made  the  statement  that  his  sensations  were  identical 
with  those  of  his  predecessor,  saying,  "That  is  exactly  like  coming 
out  of  a  spinning  nose  dive."  When  placed  in  another  position  and 
whirled  he  said,  "  Now  I  feel  like  coming  out  of  a  loop."  These  facts 
were  confirmed  by  similar  experiments  on  other  aviators. 

Since  being  whirled  in  an  aeroplane  produces  effects  identical 
with  those  resulting  from  being  whirled  in  a  laboratory  device, 
such  as  the  turning-chair,  or  other  forms  of  apparatus,  designed 
for  that  purpose,  we  are  furnished  with  an  accurate  and  convenient 
means  of  studying  the  various  vertigo  effects  of  ear  stimulation 
produced  by  evolutions  in  the  air,  and  deductions  derived  from  this 
experimental  stimulation  are  true  and  applicable  to  stunt  flying. 
The  facts  gleaned  were  so  exactly  in  accordance  with  our  knowledge 
of  the  ear  as  a  "  motion-sensing  apparatus "  that  they  were  simply 
corroborations  of  certain  well-known  otologic  principles. 

Now,  what  are  these  established  facts  or  principles  ? 

1.  In  each  ear  we  have  three  semicircular  tubes  or  canals,  contain- 
ing fluid,  so  placed  that  they  are  at  right  angles  with  each  other. 
Because  of  this  arrangement,  no  change  of  position  of  the  indi- 
vidual is  possible  without  producing  some  movement  of  fluid  in  one 
or  more  of  the  canals.    Movement  of  the  fluid  in  these  canals  sends 
messages  to  the  brain  which  are  there  interpreted  as  body  movement. 
Hence,  the  ears  constitute  the  motion-sensing  organs  of  the  body. 

2.  When  an  individual  is  whirled,  be  it  in  the  laboratory  or  in  an 
aeroplane,  there  is  produced  a  circulation  of  this  fluid  in  certain 
definite  canals  and  planes.    Now,  if  the  turning  be  suddenly  altered 
or  stopped  or  if  the  aeroplane  comes  out  of  rotating  maneuver,  the 
fluid  in  the  canals  continues  to  move  in  its  former  plane  by  sheer 

89119—18 9 


130  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

force  of  its  momentum.  This  circulation  of  the  fluid  (by  momentum) 
is  interpreted  by  the  brain  as  body  movement,  but  not  being  in  ac- 
cordance with  fact,  the  body  having  ceased  to  revolve,  constitutes 
vertigo  or  dizziness,  and  is  disturbing  to  the  individual. 

Labyrinthine  vertigo,  therefore,  is  a  false  sensation  of  motion 
similar  to  the  visual  illusion  of  motion  observed  when  watching  a 
moving  train  from  the  window  of  a  stationary  coach,  both  being 
unavoidable  phenomena  of  normal  special  sense  mechanisms,  which, 
however,  the  subject  easily  learns  to  interpret  and  disregard. 

One  must  not  fall  into  the  error,  however,  of  thinking  that  the 
lack  of  a  normal  ear  mechanism  would  be  advantageous  to  the  flier, 
because  of  the  immunity  of  vertigo  which  this  condition  would  con- 
fer. The  absence  of  such  an  essential  organ  as  a  motion-perceiving 
apparatus  is  too  great  a  handicap  to  the  man  traveling  in  an  "  air 
medium  "  even  to  think  for  a  moment  that  he  could  dispense  with  it 
for  the  sole  benefit  of  a  vertigo  immunity,  especially  since  the  normal 
individual  can  acquire  such  an  immunity  without  much  difficulty. 

VERTIGO  EFFECTS  OF  EAR  STIMULATION. 

1.  There  are  three  cardinal  planes  of  vertigo — horizontal,  frontal, 
and  sagittal. 


2.  A  sense  of  being  turned  in  a  horizontal  plane — horizontal  ver- 
tigo— is  less  disturbing  than  a  sense  of  being  whirled  in  a  vertical 
plane — vertical  vertigo.    Each  semicircular  canal,  if  stimulated,  pro- 
duces a  vertigo  in  its  own  plane.    Therefore,  with  the  individual  in 
an  upright  position,  stimulation  of  the  horizontal  canal  is  much  less 
disturbing  than  stimulation  of  the  vertical  canals. 

3.  When  a  disturbing  or  disabling  vertigo  is  induced  in  the  vertical 
semicircular  canals  the  effect  can  be  greatly  ameliorated  by  bringing 
the  vertical  canals  in  a  horizontal  position  or  plane,  which  can  readily 
be  done  by  bringing  the  head  forward. 

4.  All  types  of  vertigo,  no  matter  how  induced,  are  made  less  and 
less  disturbing  by  continual  repetition. 

PRACTICAL  APPLICATION  OF  VERTIGO  STUDY  TO  STUNT  FLYING. 

Let  us  consider  how  the  knowledge  of  the  various  effects  of  vertigo 
gained  in  the  laboratory  can  be  correlated  and  applied  to  various 
stunts. 


TIGHT  SPIRAL. 


130 


TIGHT  SPIRAL. 


TIGHT  SPIRAL. 


TIGHT  SPIRAL. 


131-1 


"  LOOPING." 
Arrow  indicates  plane  of  vertigo. 


/ 


\ 


"  LOOPING." 
Circles  indicate  plane  of  vertigo — sagittal  first,  then  frontal. 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  131 

SPINNING  NOSE  DIVE. 

In  this  maneuver  the  aviator,  face  downward,  is  whirled  about  an 
axis  with  his  head  and  body  practically  parallel  to  the  ground,  as 
shown  in  the  accompanying  sketch.  In  this  position  there  is  a  stimu- 
lation of  the  vertical  semicircular  canals  in  a  frontal  plane,  corre- 
sponding to  turning  in  the  chair  in  the  position  shown  below. 

When  he  "  comes  out "  of  the  spin,  the  plane  of  vertigo,  which  until 
now  has  been  parallel  to  the  ground,  becomes  vertical  in  a  frontal 
plane,  i.  e.,  from  side  to  side,  so  that  instead  of  feeling  that  he  is 
turning  horizontally,  he  feels  that  he  is  whirled  in  an  up  and  down 
plane;  this  being  very  disturbing,  he  is  apt  to  lose  himself  momen- 
tarily and  attempt  to  correct  this  illusionary  movement  and  so  throw 
himself  into  another  spinning  nose  dive  in  the  opposite  direction. 
When  this  same  experiment  is  carried  out  in  the  chair,  i.  e.,  when  he  is 
turned  with  his  head  forward,  simulating  his  position  during  this 
spinning  nose  dive,  and  attempts  to  sit  erect,  he  similarly  changes  his 
horizontal  vertigo,  with  which  he  started,  into  a  sensation  of  whirling 
in  an  up  and  down  plane.  In  attempting  to  correct  this  false,  impres- 
sion he  throws  his  body  to  one  side  with  such  violence  that  unless 
caught  by  the  examiner  he  would  fall  to  the  floor.  It  is  easy  to  im- 
agine what  havoc  would  be  raised  with  the  controls  of  an  airship 
under  similar  conditions.  The  obvious  remedy  in  both  cases  is  to 
keep  the  head  down,  as  it  was  in  the  beginning,  so  that  the  vertigo  re- 
mains in  the  horizontal  plane. 

TIGHT  SPIRAL. 

In  this  maneuver  the  aviator  is  whirled  about  an  axis  with  his 
head  and  body  practically  parallel  with  the  ground  but  facing  the 
horizon.  The  stimulation  occurs  in  the  vertical  canals  but  in  a 
plane  practically  parallel  with  the  ground  as  long  as  the  spiral  lasts. 
When  he  comes  out,  however,  the  plane  of  vertigo,  horizontal  until 
now,  becomes  vertical  in  a  sagittal  (from  before  backward)  plane,, 
so  that  he  feels  himself  pitching  forward  or  backward  and  may  ' 
again  meet  with  disaster  in  attempting  to  correct  for  this  illusion. 

In  the  turning-chair  this  maneuver  can  be  simulated  by  turning 
the  individual  with  his  head  sharply  inclined  over  the  shoulder  as 
illustrated. 

The  obvious  remedy  for  the  aviator  in  this  case  is  to  tilt  his  head 
sharply  to  one  side  when  coming  out  of  the  spiral,  since  by  so  doing 
he  will  prevent  the  vertigo  from  assuming  an  up  and  down  whirl. 

LOOP. 

In  this  stunt,  as  shown  in  the  accompanying  sketch,  the  vertical 
canals  are  stimulated  in  the  sagittal  plane  (as  in  the  spiral,  but  te 
a  lesser  degree).  The  correction  is  accomplished  by  tilting  the  hea4 
sharply  over  one  shoulder. 


132  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

IMMELMANN   TURN. 

In  this  evolution,  as  shown  in  the  foregoing  sketches,  we  have  a  com- 
pound maneuver.  During  the  first  or  loop  portion  the  vertical  canals 
are  stimulated  in  the  sagittal  plane,  followed  in  the  second  part  of 
the  stunt  by  a  stimulation  of  the  vertical  canals  in  the  frontal  plane. 
The  effect  of  the  first  portion  is  lost  during,  the  remainder  of  the 
stunt  so  that  on  emerging  the  aviator  has  only  to  deal  with  the  ver- 
tigo induced  by  the  last  part,  namely  vertigo  in  the  frontal  plane. 
The  obvious  correction  is  to  throw  the  head  forward  while  "  coming 
out."  In  a  similar  manner  the  vertigo  induced  by  the  "  barrel  roll," 
"  falling  leaf,"  "  wing  over,"  and  other  stunts  can  be  readily  analyzed. 

It  is,  of  course,  true  that  the  experienced  stunt  flier  is  not,  as  a  rule, 
upset  by  the  vertigo  induced  by  these  stunts  because  of  the  many 
hours  of  practice  he  has  had,  but  no  matter  how  well  trained  and 
experienced  he  may  be  he  may  occasionally  find  himself,  especially 
in  actual  combat,  doing  more  whirling  and  at  a  greater  rate  of  speed 
than  his  training  has  prepared  him  for,  and  an  understanding  of 
these  principles  might  be  the  means  of  saving  his  life.  As  a  matter 
of  fact,  stunt  fliers  develop  instinctively  certain  maneuvers  which 
neutralize  the  disabling  effects  of  vertigo;  thus  one  flier  found  by 
practical  experience  that  by  leaning  as  far  forward  as  possible,  so 
that  his  head  was  practically  inverted,  a  spinning  nose  dive  gave  him 
practically  no  disabling  vertigo.  Another  found  that  going  into  a 
straight  nose  dive  immediately  ,f ollowing  a  spinning  nose  dive  saved 
him  from  any  uncomfortable  dizziness. 

These  fliers  have  instinctively  adopted  means  which  at  all  times 
kept  the  vertigo  in  a  horizontal  plane — procedures  based  on  sound 
otologic  principles.  Experienced  aviators,  on  being  put  through  the 
various  stunts  in  the  laboratory,  when  shown  haw  easily  the  effects 
of  vertigo  are  neutralized  by  certain  changes  in  the  position  of  the 
head,  are  of  the  unanimous  opinion  that  such  knowledge  is  of  the 
greatest  practical  value,  especially  in  stunting.  It  is  obvious  that 
to  the  less  experienced  this  knowledge  is  of  even  greater  importance. 

The  greatest  usefulness  of  the  knowledge  that  "stunting"  is  an 
ear  problem  lies  in  the  fact  that  the  flier  may  be  educated  to  disre- 
gard the  vertigo  effects  of  his  stunts  in  the  laboratory  instead  of 
among  the  clouds,  and  without  danger,  acquire  a  tolerance  to  evolu- 
tions to  a  degree  impossible  in  the  air.  This  can  be  accomplished 
by  the  use  of  an  otologic  apparatus  known  as  the  Orientator.  In  its 
construction  it  is  like  the  cockpit  of  an  aeroplane  suspended  in  con- 
centric rings  after  the  manner  of  a  ship's  compass.  The  move- 
ments (or  changes  of  position)  which  are  possible  in  all  directions 
except  actual  forward  progression  are  governed  by  the  individual 
seated  in  the  machine  using  a  set  of  controls  resembling  those  of  an 


"  RUGGLES    ORIBNTATOR." 
(Supplied  through  the  courtesy  of  the  Naval  Consulting  Board.) 


132-1 


"  UUGGLES    ORIENTATOR." 
(Supplied  through  the  courtesy  of  the  Naval  Consulting  Board.) 


132-2 


"  RUGGLES    ORIENTATOR." 
(Supplied  through  the  courtesy  of  the  Naval  Consulting  Board.) 


132-3 


"  RUGGLES    ORIENTATOR." 
(Supplied  through  the  courtesy  of  the  Naval  Consulting  Board.) 


"RUGGLES  ORIENTATOR." 
(Supplied  through  through  the  courtesy  of  the  Naval  Consulting  Board.) 


132-5 


MANUAL  OP  MEDICAL  RESEARCH   LABORATORY.  133 

aeroplane.  Strapped  in  this  machine  he  is  enabled  to  execute  any 
evolution,  such  as  the  loop,  spiral,  etc.,  at  any  desired  rate  of  speed 
for  any  number  of  turns  and  thus  acquire  in  absolute  safety  a  toler- 
ance for  the  disturbing  effects  of  vertigo  induced  by  these  evolutions 
instead  of  acquiring  this  tolerance  and  knowledge  by  actual  flying 
with  its  consequent  crashes  and  possible  loss  of  life.  In  addition,  it 
will  enable  him  to  adapt  himself  to  new  and  most  unusual  conditions. 
He  will  learn  to  orientate  himself  in  new  and  rapidly  changing 
positions  of  the  body  and  to  perform  properly  the  complicated  acts 
necessary  to  control  an  aeroplane  while  flying  with  his  head  down, 
etc.,  which  entails  an  entirely  reversed  relation  to  external  objects,  a 
condition  in  itself  most  disturbing  and  pregnant  with  possibilities  of 
disaster. 

The  orientator  placed  in  the  ground-  and  flying-  schools  will  save 
manj7  lives  and  machines,  shorten  materially  the  time  of  flying  in- 
struction, and  develop  a  large  number  of  stunt  fliers. 

V.— THE  MANUAL  OF  THE  OPHTHALMOLOGICAL  DEPARTMENT 
RESEARCH  LABORATORY. 

THE  SELECTION  OF  THE  AVIATOR. 

In  answer  to  the  first  call  for  fliers  approximately  100,000  men,  the 
pick  of  the  youth  of  this  country,  applied  for  service  in  the  Aviation 
Section,  Signal  Corps,  United  States  Army.  Due  to  the  genius  for 
organization  and  tireless  energy  of  the  medical  officers  of  the  Regular 
Army,  these  men  were  carefully  examined  by  500  physicians,  work- 
ing in  67  examining  units,  and  a  sufficient  number  were  selected. 

It  is  safe  to  say  that  these  men,  by.reason  of  this  careful  method  of 
selection,  are  physically  fit,  and  it  is  well  that  this  is  the  case,  for  an 
aviator  must  not  only  be  physically  perfect  to  begin  with,  but  also 
be  kept  in  training.  It  is  certainly  more  important  to  have  an  aviator 
in  perfect  physical  condition  than  a  football  player.  Every  flier 
should  be  under  the  care  of  a  medical  man  thoroughly  trained  in  the 
care  of  the  aviator  and  the  symptoms  and  dangers  of  the  lack  of 
oxygen. 

If  we  study  for  a  moment  the  routine  employed  in  the  examination 
of  the  eye  we  will  easily  see  that  any  man  who  could  pass  these  tests 
must  have  eyes  as  nearly  perfect  as  nature  permits. 

PHYSICAL  EXAMINATION  OF  APPLICANTS  FOR  DETAIL  IN  THE  DEPARTMENT 
OF  MILITARY  AERONAUTICS. 

I.  History. — Question  the  candidate  carefully  concerning  previous 
or  present  eye  trouble,  use  of  glasses,  lachrymation,  photophobia,  and 
diplopia.  If  glasses  are  worn,  symptoms  when  not  wearing  correct- 
ing lenses. 


134  MANUAL  OF  MEDICAL  RESEARCH  LABORATORY. 

II.  Stereoscopic  vision. — The  ability  to  appreciate  depth  and  dis- 
tances by  means  of  binocular  vision.    The  ordinary  stereoscope  may 
be  used.     The  cards  should  be  clean  and  flat.    The  candidate  should 
have  a  good  light  coming  over  the  shoulder  directly  on  the  card. 
The  card  should  be  moved  back  and  forth  until  the  point  of  greatest 
distinctness  is  attained.    Have  the  candidate  name  the  sequence  of 
objects  from  before  backward,  as  he  sees  them  through  the  stereoscope. 
This  should  be  done  readily  and  without  error,  keeping  in  mind  the 
fact  that  even  though  the  usual  order  of  seeing  the  objects  on  the 
original  card  is  9-1-7,  3-2-4,  5-6-8,  and  10,  the  confusion  of  4  and  5, 
9  and  1,  and  8  and  10  occurs  in  people  with  normal  stereoscopic  vision. 
In  case  of  doubt,  use  in  addition  the  smaller  objects  on  individual 
pictures,  e.  g.,  on  No.  9  from  before  backward  is  seen  cross,  balloon, 
and  flag;  No.  8,  balloon,  cross,  rod,  and  pennant;  No.  10,  pennant, 
balloon,  and  cross.    Inability  to  stereoscope  properly  is  a  cause  for 
rejection. 

III.  Ocular  movements. — These  are  touted  roughly  by  requiring 
both  eyes  of  the  candidate  to  be  fixed  on  i  he  examiner's  finger,  which 
is  carried  from  directly  in  front  of  the  eyes  to  the  right,  to  the  left, 
up  and  down.    The  ocular  movements  must  be  regular  and  identical. 

IV.  Pupillary  reactions. — These  should  be  regular  and  equal  when 
responding  to   (1)   direct,   (2)   indirect  light  stimulation,  and   (3) 
to  accommodation.    Face  the  candidate,  who  should  be  looking  into 
the  distance,  and  place  a  card  as  a  screen  before  both  eyes.    Uncover 
one  eye  after  a  short  interval  and  allow  bright  daylight  to  shine  into 
this  eye.    The  resulting  contraction  of  the  iris  of  this  eye  is  called  a 
direct  reaction.     Repeat  the  test,  but  now  observe  the  iris  of  the 
shaded  eye.    If  this  iris  contracts,  it  is  termed  the  indirect  or  con- 
sensual reaction.    Repeat  tests  on  the  other  eye.    With  both  the  candi- 
date's eyes  open  and  uncovered,  have  him  fix  on  a  distant  object,  then 
focus  on  a  pencil  point  held  approximately  10  centimeters  in  front 
of  the  eyes.    Both  irides  should  contract,  which  is  called  the  reaction 
to  accommodation. 

V.  External  ocular  examination. — Place  the  candidate  facing  a 
good  light  and  examine  each  eye  carefully  with  the  aid  of  a  hand 
lens,  noting  any  abnormality.    The  eye  should  be  free  from  disease, 
congenital  or  acquired,  such  as  lesions  of  the  cornea,  iris,  or  lens, 
including  affections  of  the  surrounding  structures,  such  as  patho- 
logical conditions  of  the  lachrymal  apparatus,  conjunctival  deformi- 
ties, or  any  affection  which  would  tend  to  cause  blurring  of  vision 
if  the  eyes,  unprotected  by  glasses,  were  exposed  to  wind  or  other 
unfavorable  atmospheric  conditions. 

VI.  Ocular  nystagmus. — If  it  occurs  on  looking  straight  ahead 
or  laterally,  40°  or  less,  it  is  a  cause  for  rejection. 


134 


135 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  135 

(a)  Spontaneous  ocular  nystagmus  produced  by  extreme  lateral 
rotation  of  the  eyes,  50°  or  more,  is  not  a  cause  for  rejection,  as 
it  is  found  in  the  normal  individual.  It  is  usually  manifested  by 
a  few  oscillating  movements,  never  rotary,  which  appear  when  the 
eyes  are  first  fixed  in  extreme  lateral  positions.  Select  a  scleral 
vessel  near  the  corneal  margin  as  a  point  for  observation. 

VII.  Field  of  vision. — The  confrontation  test  may  be  used  to  de- 
termine roughly  the  limits  of  the  visual  field.     The  field  is  tested 
separately  for  each  eye.    Place  the  candidate  with  his  back  to  the 
source  of  light  and  have  him  fix  the  eye  under  examination  (the  other 
eye  being  covered)  upon  the  examiner's,  which  is  directly  opposite 
at  a  distance  of  2  feet.     For  example:  The  candidate's  right  eye 
being  fixed  upon  the  examiner's  left  eye;  the  examiner  then  moves 
his  fingers  in  various  directions  in  a  plane  midway  between  himself 
and  the  candidate,  until  the  limits  of  indirect  vision  are  reached. 
The  examiner  thus  compares  the  candidate's  field  of  vision  to  his 
own,  and  can  thus  roughly  estimate  whether  normal  or  not.    A  re- 
stricted field  of  vision  or  marked  scotoma  should  be  confirmed  by 
the  use  of  a  perimeter,  as  it  would  be  a  cause  for  rejection. 

VIII.  Color  vision. — Should  be  normal.     A  Jennings  test  is  re- 
quired.    If  confusion,  the  eyes  should  be  tested  with  a  Williams 
lantern.    The  Jennings  blank,  properly  filled  out,  should  form  a  part 
of  the  physical  record.     If  the  candidate  is  suspected  of  having 
learned  the  Jennings  test,  the  card  and  blank  may  be  turned  over 
and  punched  from  the  unfinished  side. 

IX.  Muscle  balance  at  20  feet. — A  phorometer,  with  spirit  level  or 
maddox  rod  and  rotary  prism  attached,  should  be  used.    Muscle  bal- 
ance is  satisfactory,  provided  there  is  not  more  than  1  degree  of 
hyperphoria,  2  degrees  of  exophoria,  or  6  degrees  of  esophoria  (if 
in  this  latter  case  there  is  a  prism  divergence  or  abduction  of  not  less 
than  6  degrees).    In  all  cases  of  heterophoria  the  duction  power  of 
the  muscles  must  be  taken  aad  recorded. 

(a)  The  screen  and  parallax  test:  In  case  the  above-described 
apparatus  is  not  available,  the  following  method  may  be  used  until 
the  proper  instruments  are  obtained : 

The  candidate  is  seated  6  meters  from  a  5-millimeter  light  on  a 
black  field  or  a  1  centimeter  black  dot  on  a  white  field,  which  he-  fixes 
intently.  Shift  a  small  card  quickly  from  eye  to  eye  and  note  any 
movement  of  the  eye  as  it  is  uncovered  and  ask  the  candidate  to  de- 
scribe any  movement  of  the  eye  or  the  light.  Orthophoria  obtains 
if  there  is  no  apparent  movement  of  the  eye  or  the  light.  Movement 
of  the  test  object  or  eye  with  the  card  signifies-  exophoria,  against  the 
card,  esophoria,  and  vertical  movement  hyperphoria.  Prisms  are 
placed  with  the  base  in  for  exophoria,  out  in  esophoria  and  up  or 


136  MANUAL  OF   MEDICAL  RESEARCH  LABORATORY. 

down  in  hyperphoria,  until  the  test  object  and  the  eye  just  begin  to 
move  in  the  opposite  direction.  The  weakest  prism  which  causes  re- 
versal of  the  movement,  minus  2  prism  degrees,  is  the  measure  of 
the  heterophoria.  If  there  are  less  than  5  degrees  of  heterophoria, 
only  1  prism  degree  is  subtracted. 

(&)  Near  point  of  convergence:  A  2-millimeter  white-headed  pin 
or  a  1 -millimeter  black  dot  on  a  white  card  is  carried  toward  the 
subject  along  a  millimeter  rule  from  a  distance  of  50  centimeters,  and 
the  point  noted  at  which  one  or  both  eyes  cease  to  fix  or  diplopia  is 
first  noted  by  the  candidate.  This  point  is  measured  in  millimeters 
from  the  anterior  surface  of  the  cornea.  Keep  the  test  object  in  the 
mid  line,  a  few  degrees  below  the  horizontal  plane.  A  near  point 
greater  than  65  millimeters  at  25  years  of  age,  and  85  millimeters  at 
30  years  of  age  is  a  cause  for  disqualification. 

X.  Visual  acuity. —  (a)  Acuity  for  distance:  Test  each  eye  sepa- 
rately, 20  feet  from  a  well-illuminated  card  with  Snellen  letters. 
Full  twenty  twentieths  vision  in  each  eye  is)  desired,  but  a  candidate 
may  be  allowed  to  miss  three  letters  on  the  20/20  line  with  one  eye, 
provided  the  other  has  full  20/20  vision,  and  all  other  tests  are  nor- 
mal.    Visual  acuity  should  be  taken  without  the  use  of  correcting 
lenses. 

Place  a  plus  2.00D  sph.  before  each  eye  successively  while  the  other 
eye  is  covered.  A  candidate  who  can  still  read  20/20  with  either  eye 
is  disqualified. 

(b)  Near  point,  or  acuity  for  near  vision  is  determined  separately 
for  each  eye  by  requiring  the  candidate  to  read,  in  a  good  light, 
Jaeger  test  type  No.  1,  gradually  bringing  the  card  toward  the  un- 
covered eye  until  the  first  blurring  of  the  print  is  noted. 

The  distance  of  this  point  from  the  anterior  surface  of  the  cornea, 
measured  in  centimeters,  is  the  near  point.  A  distance  greater  than 
11  centimeters  at  19  years  of  age,  greater  than  13  centimeters  at  2f> 
years  of  age,  or  greater  than  15  centimeters  at  30  years  of  age,  dis- 
qualifies. 

XI.  Ophthalnwscopic  findings. — Drop  one  drop  of  a  5  per  cent 
solution  of  euphthalmin  in  each  eye.     Have  the  candidate  keep  his 
eyes  closed.     After  15  minutes  repeat  the  drops,  then  examine  15 
minutes  later.     A  solution  of  cocaine,  4  per  cent,  may  be  substituted, 
cautioning  the  candidate  to  keep  his  eyes  closed  between  installa- 
tions.    A  pathological  condition  of  the  fundus,  active  or  quiescent, 
is  a  cause  for  rejection. 

VALUE  OF  THE  EYE  IN  AVIATION. 

I.  Judgment  of  distance. — Judgment  of 'distance  is  assisted  by  the 
power  of  stereoscopic  vision,  and  for  this  reason  the  eyes  of  all 
candidates  for  admission  into  the  Aviation  Section,  Signal  Corps 


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137 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  137 

of  the  United  States  Army,  have  had  their  binocular  vision  tested  by 
means  of  a  stereoscope.  Inability  to  stereoscope  quickly  and  accu- 
rately is  considered  a  cause  for  disqualification.  We  know  that  if  a 
man  loses  one  eye  he  is  often  able  to  judge  distance  very  accurately 
with  the  remaining  one,  but  it  requires  time  for  him  to  develop  this 
power.  It  would  therefore  seem  logical,  at  least  while  we  are  able 
to  select  our  men  carefully,  to  accept  only  those  with  normal  stereo- 
scopic vision. 

Speaking  of  error  of  judgment  in  flying  as  a  cause  of  aeroplane 
accidents,  Anderson  states  that  this  error  may  occur  in  getting  off 
the  ground,  in  the  air,  or  when  landing.  Of  the  58  crashes  in  the 
"'  V  "  series,  this  cause  accounted  for  42 — 4  in  getting  off  the  ground 
and  38  in  landing. 

Of  the  many  examples  of  error  in  judgment  in  flying,  perhaps 
the  commonest  is  when,  on  landing,  the  pupil  misjudges  his  distance 
from  the  ground  and  either  flattens  out  too  soon  and  "  pancakes," 
with  a  possible  crash,  depending  on  the  height,  or  else  flattens  out 
too  late  and  strikes  the  ground  at  a  great  angle,  usually  overturning 
and  wrecking  the  machine. 

It  is  difficult  to  estimate  and  account  for  these  errors  of  judgment. 
In  some  cases  it  may  be  due  to  insufficient  instruction.  In  other 
cases,  even  after  prolonged  instruction,  the  pupil  may  still  misjudge 
distance,  and  on  examination  one  occasionally  finds  that  his  standard 
of  vision  is  below  normal ;  but.  on  the  other  hand,  he  may  be  found 
physically  fit,  with  normal  vision  and  normal  muscle  balance.  In 
the  latter  case  Anderson  believes  it  may  be  a  question  of  delayed 
reaction  time,  and  especially  the  visual  reaction  time,  upon  which 
the  aviator  is  so  much  dependent.  Normally  this  reaction  time  is 
nineteen  one-hundredths  or  twenty  one-hundredths  of  a  second.  It 
may  be  delayed  by  fatigue  and  excesses,  but  in  some  individuals  who 
are  otherwise  physically  fit  it  is  found  to  be  much  slower  than  in 
others. 

Hence,  in  the  selecting  of  candidates  for  aviation  the  visual  and 
other  reaction  times  should  be  normal.  By  the  French  medical  au- 
thorities on  aviation  candidates  are  rejected  if  simple  reaction  times 
are  found  to  be  of  the  delayed  type.  The  Italians  also  seem  to  lay 
considerable  stress  upon  simple  reaction  time.  The  men  who  have 
done  the  most  work  in  reaction  time  in  this  country,  are  of  the 
opinion  that  simple  reaction  time  is  of  little  value  in  the  selection  of 
candidates  for  aviation.  The  accurate  determination  of  the  visual 
discrimination  reaction  time  and  other  complex  reaction  times  might 
be  of  considerable  value.  It  would  seem  as  though  physical  condition 
on  a  given  day  and  the  added  strain  of  low  oxygen  tension  should  be 
taken  into  consideration  in  seeking  the  cause  of  these  accidents.  We 
know  that  there  might  be  a  temporary  visual  disturbance  or  weaken- 


138  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

ing  of  the  external  ocular  muscles,  and  this  might  account  for  some 
of  the  accidents.  Naturally,  examination  of  the  eyes  later  on  might 
show  nothing. 

II.  Normal  visual  acuity, — As  long  as  we  can  in  this  country  select 
only  those  men  with  practically  perfect  vision  it  would  seem  well 
to  do  this.    A  man  with  poor  vision  will  not  be  able  to  see  an  enemy 
plane  as  soon  as  a  man  with  perfect  vision.    He  will  not  be  able  to 
accurately  differentiate  objects  seen  from  the  air  in  selecting  a  land- 
ing place,  and  when  he  has  reached  the  ground  he  will  not  see  ob- 
structions in  his  path  as  clearly  as  he  should.    The  latter  may  result 
in  the  plane  being  "nosed  over."     In  a  recent  discussion  of  the 
"  Physical  Qualities  of  Aviators  "  all  the  British  officers  and  physi- 
cians taking  part  agreed  that  the  factor  of  vision  was  of  the  greatest 
importance,  and  Clark  pled  for  the  use  of  a  cycloplegic  in  making 
examinations  for  admission  to  the  flying  corps.     During  the  low 
oxygen  tension  test  visual  acuity  diminished  in  28  per  cent  of  the 
normal  men  examined  and  in  37.5  per  cent  of  the  men  who  were 
ocularly  disqualified  for  flying. 

III.  Normal  color  vision. — It  is  important  that  the  flier  have  nor- 
mal color  vision  in  order  that  he  may  accurately  determine  the 
markings  of  the  different  planes,  differentiate  between  signal  lights, 
and  in  helping  him  to  make  landings  at  night.    During  the  day  the 
discrimination  between  the  color  of  a  building,"field,  forest,  or  swamp 
is  essential  in  selecting  a  landing  place.    There  has  been  no  change 
in  color  vision  during  the  rebreathing  test  or  in  the  low-pressure 
chamber. 

IV.  Field  of  binocular  fixation. — It  is  important  that  the  aviator 
be  able  to  carry  the  eyes  as  far  as  possible  in  various  directions 
without  turning  his  head  and  without  seeing  double.    If  a  man  has 
a  contracted  binocular  field  of  vision,  it  certainly  impairs  his  effi- 
ciency, whether  observing,  fighting,  or  flying.     In  50  per  cent  of 
the  subnormal  men  examined  during  the  low  oxygen  tension  test  we 
have  found  contraction  of  the  field  of  binocular  fixation,  the  con- 
traction being  most  marked  in  the  upper  field. 

V.  Muscle  balance. — Normal  muscle  balance  should  be  insisted 
upon,  for  even  a  small  defect  may  be  accentuated  by  the  strain  of 
flying  and  lack  of  oxygen  and  result  in  diplopia  or  at  least  a  marked 
contraction  of  the  field  of  binocular  vision  at  low  altitudes.     Ex- 
ophoria  and  hyperphoria  have  been  shown  to  be  the  most  important, 
due  to  the  fact  that  the  weakness  of  the  ocular  muscles  caused  by 
the  lack  of  oxygen  produces  diplopia  more  readily  in  exophoria  and 
hyperphoria  than  in  esophoria. 

VI.  Field  of  vision. — The  field  of  vision  should  be  normal,  as  the 
aviator's  safety  depends  to  a  great  extent  upon  his  ability  to  detect 


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MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


139 


enemy  planes  or  in  training  his  own  plane  in  the  various  fields  while 
his  gaze  is  fixed  straight  ahead.  The  aeroplane  and  the  goggle  also 
do  harm  in  that  they  restrict  the  field  of  vision,  and  many  accidents 
result  from  this.  Everything  should  be  done  to  improve  the  con- 
struction of  goggles  and  planes  so  that  the  visual  field  will  be  re- 
stricted as  little  as  possible. 

VII.  The  perception  of  motion  and  its  direction. — The  perceptior 
of  motion  and  its  direction  is  of  great  importance  to  the  aviator. 
Appropriate  tests  for  measuring  this  have  been  devised.  The  best 
pilots  say  that  they  finally  develop  the  power  to  use  the  periphery 
of  the  retina  so  that  it  is  of  greater  value  in  detecting  enemy  planes 


VIII.  The  importance  of  the  eye  in  maintaining  equilibrium. — 
Before  going  into  this,  first  let  it  be  stated  that  the  subject  of  equi- 
libration is  a  complex  one  and  that  those  of  us  who  have  an  interest 
in  it  from  a  practical  standpoint  appreciate  the  difficulty  of  the 
subject  and  realize  that  although  the  aviator  may  fly  when  one  part 
of  this  mechanism  is  deranged  or  destroyed,  we  believe  that  in  select- 
ing men  for  flying  positions  that  it  is  well  to  make  sure  that  all  the 
senses  used  in  this  complex  act  are  normal.  The  most  important 
factors  in  receiving  impressions  are  deep  sensibility,  tactile  sense,  the 


140  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

vestibular  apparatus,  and  the  eyes.  The  central  nervous  system  con- 
nections must  functionate  perfectly  to  use  the  information  it  receives 
to  the  best  advantage.  Finally,  the  muscles  should  be  in  condition 
to  carry  out  the  commands  of  the  central  nervous  system. 

That  many  aviators  depend  largely  upon  their  visual  impressions 
in  the  maintenance  of  equilibrium  is  evidenced  by  the  fact  that  they 
often  tie  a  piece  of  string  as  a  streamer  to  one  of  the  forward  struts, 
so  that  they  may  more  readily  note  the  first  evidence  of  a  side  slip 
when  they  are  flying  in  a  cloud.  In  spite  of  the  fact  that  we  miss  the 
visual  impressions  when  they  are  not  received,  we  are  still  able  to 
control  the  plane  if  the  remainder  of  the  balance  mechanism  is 
functioning  normally. 

IX.  Retinal  sensitivity  to  light. — It  is  important  that  the  retina 
be  sensitive  to  light  impressions,  especially  for  those  men  who  are 
carrying  out  night  bombing  expeditions.  With  this  in  mind,  most 
of  the  allied  nations  require  special  tests  for  retinal  sensitivity.  A 
test  of  the  contrast  sensitivity  of  the  retina  is  believed  to  be  the  most 
useful  for  our  work,  and  only  men  who  have  normal  sensitivity  in 
this  respect  will  be  selected  for  night  flying. 

THE  CARE  OF  THE  FLIER  AND  THE  EFFECT  OF  ALTITUDE  AND  THE  STRAIN 
OF  FLYING  ON   THE  EYE. 

Even  though  our  aviators  have  been  examined  with  the  greatest 
care  and  their  eyes  are  as  nearly  perfect  as  nature  permits,  the  adapt- 
ing mechanism  of  the  human  machine,  including  the  eye,  was  de- 
signed for  use  on  earth,  and  altitude  adds  an  unusual  strain.  Medi- 
cal men  agree  that  definite  physiologic  changes  occur  in  man  living 
at  high  altitudes  which  permit  them  to  withstand  lack  of  oxygen, 
but  they  believe  from  the  examinations  that  have  been  made  of  fliers 
that  they  do  not  become  acclimated,  but  often  show  rather  rapid 
physical  deterioration. 

The  most  important  ocular  symptom  is  failing  vision.  The  pilot 
complains  that  he  can  not  see  the  ground  clearly  in  landing  and  has 
difficulty  in  picking  out  enemy  planes.  There  may  be  no  defect  in 
vision,  but  there  is  usually  some  slight  error  which  was  previously 
correctable  by  an  unconscious  muscular  effort.  The  muscles  become 
fatigued,  due  to  the  strain  of  flying,  and  the  defect  shows  itself.  A 
few  days'  rest  has  been  sufficient  in  the  few  cases  Maj.  James  L.  Bir- 
ley,  R.  A.  M.  C.,  has  seen,  to  restore  normal  vision. 

Certain  individuals  with  apparent  perfect  acuity  of  vision  are 
ocularly  weak  in  that  they  are  unable  to  make  use  of  both  eyes,  due 
to  some  defect  in  binocular  vision  or  fusion  sense.  This  interferes 
somewhat  with  judgment  of  distance,  and  the  disability  tends  to 
increase  tinder  the  strain  of  aviation  and  lack  of  oxygen,  resulting  in 


JOHNSON  VISUAL  ACUITY  TESTING  APPARATUS. 


Lieut.  Johnson's  visual  acuity  test  with  subject  on  rebreathing  apparatus. 
Oxygen  at  end  of  experiment,  10%.  Lo\ver  parts  of  curve  indicate  maximal 
vision.  Subject  observes  test  object  for  periods  of  three  minutes,  with  one 
minute  intervals  of  rest. 


Test  object  observed  during  periods  of  three  minutes  with  one  minute  intervals 
of  rest.  Amyl  nitrite  (2  minims)  inhaled  during  third  period.  Lower  ex- 
cursions of  curve  indicate  clearer  vision. 


1  *-  , 

1  *-  . 

«  -* 

i  -  * 

•  * 

-  .  * 

CADET  D.  W.  MILLS,  5/9/18. 


140 


141 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  141 

bad  landings,  "  crashes,"  and  consequent  loss  of  personnel  and  mate- 
rial.   These  conditions  may  often  be  improved  by  treatment. 

Irritation,  congestion,  and  inflammation  of  the  conjunctiva  and 
epiphora  were  common  complaints  of  the  fliers  at  Chanute  Field. 
Most  aviators  realize  the  necessity  for  wearing  goggles,  but  many  of 
them  fit  poorly,  allowing  the  cold  air  to  strike  the  eye  with  great 
force,  most  often  near  the  internal  canthus  where  the  lachrymal 
puncta  are  situated.  This  probably  accounts  for  the  disagreeable 
symptoms  noted.  The  remedy  is  found  in  the  wearing  of  properly 
fitted  goggles  and  the  use  two  or  three  times  daily  of  a  2  per  cent 
boric  acid  solution  containing  1  grain  of  zinc  sulphate  to  the  ounce. 
In  some  instances  1  grain  of  cocaine  and  10  to  30  minims  of  1-to- 
1,000  adrenalin  chloride  may  be  added  to  the  ounce. 

GOGGLES. 

I.  The  glass — 

(a)  Should  have  an  optically  plane  surface. 

(b)  Should  have  a  light  transmission  of  90  per  cent  or  over  for 
plain  white  glass. 

(c)  If  a  colored  glass  is  desired.  No  viol  "  C,"  made  by  the  Corning 
Manufacturing  Co.,  of  New  York,  with  a  light  transmission  of  87 
per  cent,  is  excellent.    Euphos  has  given  great  comfort  and  the  glass 
passes  a  good  test.    The  retina  of  the  eye  is  sensitive  to  the  glare,  and 
that  is  probably  one  of  the  causes  for  physical  fatigue  of  the  aviator. 
The  colored  lenses  shut  out  most  of  the  ultraviolet  rays,  and  some 
consider  them  of  great  value  in  bright  sunlight,  in  snow,  on  water, 
and  above  the  clouds.   Many  aviators  object  to  any  tint  in  their  lenses, 
due  to  the  fact  that  they  say  they  are  unable  to  see  as  well  in  a  fog 
and  that  the  color  in  the  lenses  changes  the  color  of  objects  looked 
at,  especially  the  German  uniform  and  the  fields  in  making  landings, 
resulting  sometimes  in  the  selection  of  poor  landing  places  or  in  the 
mis  judgment  of  distance. 

(d)  Thickness  of  the  glass :  The  lenses  should  be  2  or  3  millimeters 
thick. 

(e)  Many  aviators  insist  upon  some  form  of  so-called  nonbreak- 
able  glasses,  which  is  nothing  more  than  two  pieces  of  glass  with  a 
piece  of  celluloid  between.     This  piece  of  celluloid  cuts  down  the 
transmission  of  light  between  16  and  19  per  cent,  and  no  matter  how 
clear  the  celluloid  is  originally,  it  deteriorates  with  age  and  becomes 
yellow  and  less  transparent.     When  these  glasses  are  struck  with 
considerable  force  the  glass  on  the  posterior  surface  splinters  off  and 
flies  into  the  eye.    Even  with  these  disadvantages,  some  men  insist 
upon  the  nonbreakable  feature,  and  perhaps  not  without  reason,  for 
even  though  the  splinters  do  fly  off  the  back  of  the  glass,  the  eye 
closes  immediately  in  an  accident,  and  these  small  particles  would 


142  MANUAL  OP  MEDICAL  BESEAECH   LABOBATOEY. 

hardly  penetrate  the  lids,  and  there  is  no  doubt  that  in  some  instances 
the  celluloid  prevents  the  driving  of  large  pieces  of  glass  toward 
the  eye. 

II.  Visual  field. — It  is  most  important  that  the  aviator  have  a 
broad  field  of  vision,  and  for  this  reason  a  large  curved  glass  is  desir- 
able.   Without  a  broad  field  of  vision  the  aviator  may  not  see  one  of 
his  own  planes  in  time  to  prevent  an  accident.    Pilots  who  are  doing 
actual  fighting  demand  a  broad  visual  field  above  everything  else. 

III.  Visual  acuity. — It  is  important  that  the  aviator  have  keen 
vision,  and  for  this  reason  glass  with  optically  plane  surfaces  should 
be  furnished  and  a  determination  made  of  how  much  visual  acuity  is 
cut  down  by  celluloid. 

IV.  Safety  to  the  eye. — The  parts  of  the  goggle  which  come  in  con- 
tact with  the  brow,  nose,  and  cheeks  should  have  round  edges  and 
be  protected  by  a  soft  cushion. 

V.  Lightness  and  strength. — The  goggles  should  be  light,  so  that 
they  will  not  cause  discomfort.     They  should  be  simple  in  con- 
struction and  yet  strongly  made. 

VI.  Comfort. — The  goggles  should  not  press  upon  the  bridge  of 
the  nose  so  as  to  produce  pain,  and  the  elastic  which  holds  the 
goggles  in  place  should  not  be  drawn  too  tight.    An  adjustable  inter- 
pupillary  distance  might  be  valuable. 

VII.  Cleansing. — Goggles   should   be   easily   cleaned,   and   there 
should  be  no  place  for  vermin  to  hide. 

IX.  Protecting  sinuses. — There  should  be  sufficient  covering  in 
connection  with  the  goggles  to  protect  the  frontal  sinus.    Aviators 
often  complain  of  pain  in  this  region  when  it  is  left  exposed. 

X.  Ventilation. — The  goggles  should  be  carefully  adjusted  so  that 
there  are  no  leaks,  especially  near  the  nose,  which  would  permit  the 
wind  to  strike  the  internal  canthi  directly.     Most  of  the  aviators 
who  have  done  fighting  at  high  altitudes  believe  that  the  goggles 
should  be  equipped  with  some  indirect  method  of  ventilation. 

XI.  Material  for  lenses. — Glass  is  best.     Celluloid  and  gelatin 
smear  too  easily  and  celluloid  deteriorates  too  rapidly.    Mica  chips 
and  cracks. 

XII.  Noninflammable. — The   material    of   which   the    goggle   is 
composed  should  be  noninflammable  and  for  this  reason  any  wooly 
material  is  dangerous,  as  it  burns  readily.    Incendiary  bullets  are 
now  being  used,  and  they  cause  great  damage  when  they  strike  a  gas 
tank. 

XIII.  To  further  prevent  injury  to  the  aviator,  all  parts  of  the 
fuselage  or  control  system  which  he  is  liable  to  strike  in  falling 
should  be  protected  by  pneumatic  cushions. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  143 

"  Doctors  and  professional  aviators  have  noticed  that  during  the 
ascent  respirations  become  more  rapid  and  the  heart  beats  faster 
up  to  an  altitude  of  1,500  meters.  At  this  altitude  the  vision  may 
become  less  clear,  although  a  French  observer  states  that  at  2,000 
meters  the  visual  acuity  usually  increases  by  a  third  by  reason  of  the 
congestion  of  all  the  organs  of  the  head  and  in  particular  of  the 
choroid  and  of  the  retina."  Visual  acuity  tests  carried  out  under 
low-oxygen  tension  on  the  rebrea thing  apparatus  and  in  the  low- 
pressure  chamber  have  not  shown  any  marked  increase  in  vision. 
On  the  contrary,  the  improvement,  when  it  occurred,  has  usually 
been  slight,  but  more  often  the  vision  has  remained  unchanged  and 
in  a  few  cases  has  fallen  off  considerably. 

"  During  the  descent,  there  is  another  series  of  phenomena  which 
increases  as  one  approaches  the  ground.  It  is  first  the  sensation  of 
smarting  of  the  face  with  redness  and  very  high  color.  The  eyes 
sting  and  are  injected.  The  nostrils  are  moist  and  then  comes  a 
headache,  or  more  exactly  a  sort  of  heavy  feeling  in  the  head  with  a 
sensation  of  obstruction.  Swelling  in  the  pharynx  at  the  level  of 
the  larynx.  Finally  there  is  a  strong  tendency  to  sleep." 

"  To  explain  these  difficulties  during  the  descent,  one  may  admit 
that  an  airman  who  falls  to  the  earth  in  four  or  five  minutes  or 
less,  after  having  attained  3,000  or  4.000  meters  of  elevation  in  20 
minutes,  had  not  had  time  to  adapt  his  circulatory  system  to  the 
different  barometric  pressures."  From  the  experimental  work  done, 
the  change  in  oxygen  tension  would  seem  to  be  the  most  important 
factor  in  the  production  of  symptoms. 

The  question  of  correcting  lenses  is  an  important  one  and  most 
ophthalmologists  feel  that  it  is  better  in  principle  not  to  have  vision 
corrected  by  lenses,  at  least  as  long  as  we  are  able  to  obtain  men 
with  nearly  perfect  vision.  The  aviator  needs  perfect  vision  and  a 
normal  ability  to  distinguish  colors,  a  rapid  valuation  of  distances 
and  the  faculty  of  accommodating  rapidly.  There  have  been  many, 
accidents  described  as  due  to  hyperopia,  myopia,  and  astigmatism, 
and  it  is  a  question  if  it  would  not  be  well  to  use  a  cycloplegic  in  the 
examination  of  all  candidates  for  admission  to  the  flying  corps. 

The  research  work  done  in  this  laboratory  has  shown  definitely 
that  a  flier's  life  depends,  to  a  great  extent,  upon  his  ability  to  keep 
in  condition,  both  mentally  and  physically.  Loss  of  sleep,  dissipa- 
tion, or  illness  will  so  lower  his  resistance  that  his  eyes  break  more 
readily  under  the  added  strain  of  low-oxygen  tension,  which,  in  actual 
flying,  would  frequently  result  in  death. 

When  every  flier  understands  this  fact  we  will  have  a  more  effi- 
cient flying  corps  and  fewer  accidents. 


144 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 


345 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  145 

OPHTHALMOLOGICAL   EXAMINATION    OF   THE   FLIER    DURING   LOW-OXYGEN 

TENSION  EXPERIMENT. 

PBELIMINAEY. 

Visual  acuity. — A  Snellen  test  card  is  hung  on  a  level  with  the  can- 
didate's eyes,  at  a  distance  of  20  feet.  Uniform  illumination  is  ob- 
tained by  the  use  of  a  75-watt  nitrogen  daylight  lamp,  placed  1  foot 
from  the  card,  at  an  angle  of  45  degrees. 

The  left  eye  is  covered  and  the  vision  of  the  right  eye  recorded  in 
feet.  (Ex.  20/20,  or  if  three  letters  are  missed  in  the  20/20  line, 
20/20-3.)  The  right  eye  being  covered,  the  vision  of  the  left  eye  is 
determined  and  recorded  in  the  same  manner.  Place  a  trial  frame 
before  the  eyes  and  cover  the  left  eye,  place  a  high  plus  sphere  before 
the  right  eye  and  add  minus  spheres  until  the  best  line  read  without 
the  use  of  a  lense  is  again  distinct.  This  procedure  is  repeated  for  the 
left  eye,  and  the  strongest  convex  lens  which  still  permits  clear  vision 
is  recorded. 

RETINAL    SENSITIVITY. 

A.  Contrast  sensitivity. —  (1)  This  is  the  test  to  be  used  in  the 
routine  preliminary  examination.  The  test  object  is  made  by  pasting 
a  1-inch  square  of  gray  paper  on  a  2-inch  square  of  lighter  gray  paper 
where  there  are  13  perceptible  differences  between  the  two  squares. 
The  two  squares  are  mounted  on  a  5-inch  square  of  heavy  cardboard 
for  handling.  The  test  object  is  placed  slightly  above  the  level  of 
the  subject's  eyes  at  a  distance  of  20  feet.  A  75-watt,  110-Tolt  day- 
light lamp  at  a  distance  of  &|  inches  and  at  an  angle  of  45  degrees  is 
used  to  illuminate  the  test  object.  The  Keeve's  wedge  is  made  by 
coating  a  neutrally  dyed  gelatine  in  a  wedge  shape  on  plate  glass  so 
that  the  absorption  of  light  varies  with  the  thickness  of  gelatine  de- 
posit. A  cover  glass  is  cemented  over  the  gelatine  for  protection. 
The  subject  is  told  the  principle  of  the  wedge  and  what  to  look  for 
when  viewing  the  test  object  through  the  wedge.  Before  making 
any  readings  the  subject  should  be  shown  how  to  keep  his  pupil  in  line 
with  the  aperture  in  the  wedge  case.  The  subject,  with  both  eyes 
open,  then  draws  the  wedge  from  its  case  until  the  contrast  just  dis- 
appears and  the  larger  square  appears  uniform.  When  the  pupil  is 
in  line  the  examiner  should  give  the  word  for  the  wedge  to  be  drawn 
out  of  the  holder.  The  rate  of  movement  should  be  so  regulated 
that  the  contrast  disappears  in  not  less  than  five  nor  more  than  eight 
seconds.  Repeat  until  three  readings  have  been  obtained  and  if  these 
results  are  not  too  discordant  their  average  represents  the  threshold 
for  the  subject. 

(2)  A  20/50  Snellen  illiterate  "  E  "  is  used  instead  of  the  smaller 
square  and  the  subject  should  be  able  to  tell  which  direction  the  "  E  " 
89119—18 10 


146  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

points  when  it  is  shifted — as  he  observes  it  through  the  wedge.  This 
test  is  to  be  used  in  special  cases ;  suspected  malingering,  etc. 

B.  Threshold  sensitivity. — This  procedure  may  be  employed  to 
check  the  contrast  sensitivity  test. 

At  the  regular  distance  of  20  feet,  with  the  Beeves  wedge  before 
the  right  eye,. the  observer  looks  at  a  3-millimeter  aperture  in  the 
iris  diaphragm  on  the  De  Zeng  stand.  A  36-watt  110-volt  Mazda 
lamp  with  a  frosted  globe  is  used  as  the  source  of  illumination,  the 
candidate  looking  through  the  aperture  in  the  wedge  with  the  right 
eye.  The  wedge  is  drawn  out  until  the  light  just  becomes  invisible, 
the  rate  of  movement  to  be  the  same  as  in  the  determination  of 
contrast  sensitivity.  The  reading  of  the  scale  on  the  wedge  repre- 
sents the  threshold  for  the  adaptation  to  the  brightness  of  the  room. 
(The  absolute  threshold  would  be  represented  by  a  similar  procedure 
when  the  eyes  were  completely  adapted  to  a  total  darkness.)  At 
least  three  readings  should  be  taken  for  this  threshold  and,  if  the 
results  are  too  discordant,  the  examiner  should  repeat  directions  and 
closely  supervise  the  procedure.  When  giving  directions,  the  ex- 
aminer is  getting  the  aperture  in  the  wedge  apparatus  centrally 
aligned  with  the  pupil.  This  threshold  value  represents  the  least 
that  can  be  seen  for  the  particular  adaptation  of  the  retina.  (The 
examiner  should  always  bear  in  mind  that  the  threshold  value  differs 
greatly  for  different  brightness  adaptations  and  different  states  of 
adaptation  to  the  same  brightness.)  The  average  reading  for  the 
wedge  should  be  determined  for  special  conditions  found  at  each 
laboratory.  If  the  eye  is  to  be  adapted  in  an  absolutely  dark  room, 
for  practical  purposes,  the  adaptation  would  be  complete  in  20 
minutes.  If  the  candidate  is  to  be  adapted  for  a  light  room  of 
known  brightness,  for  instance,  a  75-watt  nitrogen  daylight  lamp  in 
a  dark  room,  15  by  10  b}^  8  feet,  5  minutes'  adaptation  would  be 
sufficient. 

MUSCLE   BALANCE — THE  EOUTINE. 

The  subject's  eyes  should  be  on  a  level  with  and  directly  facing  a 
1-centimeter  black  dot  on  a  white  card  or  the  1  centimeter  opening  in 
the  iris  diaphragm  on  the  De  Zeng  stand,  20  or  25  feet  distant.  It 
is  most  important  to  see  that  the  candidate's  head  is  held  in  the 
vertical  plane  if  errors  in  determining  the  amount  of  hyperphoria 
are  to  be  avoided.  If  a  phorometer  or  Maddox  rod  is  used,  it  is 
well  to  check  the  findings  with  the  screen  and  parallax  test. 


MADDOX  BOD  TEST. 


A  trial  frame  with  a  red  multiple  Maddox  rod,  properly  centered 
before  the  right  eye,  should  be  carefully  adjusted  so  that  there  is  no 
sagging  from  the  horizontal  plane.  The  eyes  are  fixed  on  the  light 
source  and  the  left  eye  is  covered  to  make  sure  that  the  single  bar 


147 


MANUAL   OF    MEDICAL  RESEARCH   LABORATORY.  147 

of  light  is  accurately  observed,  running  horizontally,  when  the  rod 
is  vertical,  and  vertically  when  the  rods  are  horizontal.  The  left  eye 
is  uncovered  and  the  candidate  states  the  exact  position  of  the  red 
line  in  relation  to  tlie  light.  If  the  red  line,  when  vertical  and  hori- 
zontal, runs  directly  through  the  light  orthophoria  obtains  for  dis- 
tance. If  the  vertical  red  line  is  to  the  left  of  the  lights  (crossed 
diplopia)  there  is  exophoria.  If  the  line  is  to  the  right  of  the  lights 
(homonymous  diplopia)  there  is  esophoria.  The  prism,  placed  base 
in  before  the  left  eye  in  exophoria  and  base  out  in  esophoria,  which 
causes  the  line  to  run  through  the  lights  is  the  measure  of  the  hori- 
zontal imbalance.  If  the  horizontal  line  is  above  the  light  there  is 
left  hyperphoria;  if  below  the  light,  right  hyperphoria;  and  the 
prism,  base  up  or  down,  which  causes  the  line  to  run  through  the 
light,  is  the  measure  of  the  vertical  imbalance.  To  remember  that 
high  eye  means  low  image;  and,  when  the  eyes  are  uncrossed,  the 
diplopia  is  crossed,  may  help  one  in  the  study  of  the  heterophorias. 

Some  candidates  may  not  understand  the  rod  test,  or  they  may  have 
been  coached  to  say  that  the  rod  runs  through  the  light,  so  always 
check  the  findings  with  the  screen  and  parallax  test  or  use  the  rod  in 
combination  with  a  prism  which  would  produce  a  known  deviation 
of  the  line. 

SCREEN  AND  PARALLAX  TEST. 

The  candidate  is  seated  6  meters  from  a  1 -centimeter  light  on  a 
black  field  or  a  1-centimeter  black  dot  on  a  white  field,  which  he 
fixes  intently.  Shift  a  card  quickly  from  eye  to  eye  and  note  any 
movement  of  the  eye  as  it  is  uncovered  and  ask  the  candidate  to 
describe  any  movement  of  the  eye  or  the  light.  Orthophoria  obtains 
if  there  is  no  apparent  movement  of  the  eye  or  the  light.  Movement 
of  the  test  object  or  eye  with  the  card  signifies  exophoria;  against 
the  card,  esophoria;  and  vertical  movement,  hyperphoria.  Prisms 
are  placed  with  the  base  in  for  exophoria,  out  in  esophoria,  up  before 
the  right  eye  in  left  hyperphoria,  and  down  in  right  hyperphoria, 
until  the  test  object  and  the  eye  just  begin  to  move  in  the  opposite 
direction.  The  weakest  prism  which  causes  reversal  of  movement, 
minus  2  prism  degrees,  is  the  measure  of  the  heterophoria.  If  there 
is  less  than  5  degrees  of  heterophoria,  only  1  prism  degree  is  sub- 
tracted. 

N.  B. — In  hyperphoria  first  correct  the  horizontal  imbalance  and 
then  superimpose  the  square  prisms  to  determine  the  amount  of  verti- 
cal imbalance.  The  prism  which  just  stops  the  movement  gives  the 
measure  of  the  hyperphoria. 

If  muscle  imbalance  of  more  than  1  degree  is  found  in  either  plane, 
the  Maddox  rod  and  screen  and  parallax  tests  should  be  made  at  14 
inches,  using  a  2-millimeter  black  dot  on  a  white  card  or  the  light  of 


148  MANUAL   OF    MEDICAL  RESEARCH   LABORATORY. 

the  Hare-Marple  ophthalmoscope  as  the  test  object.  The  converging, 
diverging,  and  sursumverging  power  should  also  be  taken  and  re- 
corded on  back  of  the  5  by  8  history  card. 

Example. — In  testing  the  power  of  convergence  the  subject  fixes  the 
1-centimeter  black  dot  at  20  feet,  and  prisms  of  increasing  strength 
are  placed,  base  out,  before  either  eye  until  the  diplopia  produced 
can  not  be  overcome.  The  strongest  prism  through  which  binocular 
single  vision  is  obtained  is  the  measure  of  the  converging  power. 
Practice  is  important,  especially  in  determining  the  power  of  con- 
vergence. It  is  well  to  begin  with  a  very  Aveak  prism  and  gradually 
increase  the  strength,  permitting  the  subject  to  close  his  eyes  and  then 
open  them  quickly  when  he  has  difficulty  in  fusing  the  test  object. 
In  testing  the  diverging  power,  prisms  are  placed  base  in  and  gradu- 
ally increased  in  strength.  To  make  certain  that  the  candidate  is 
really  fusing,  the  prism  may  be  rotated  a  little,  producing  a  vertical 
diplopia,  and  then  brought  back  to  the  horizontal,  or  the  eyes  may 
be  screened  alternately  and  any  movement  of  the  unscreened  eye 
noted.  The  right  sursumverging  power  is  tested  with  the  prism  base 
down.  Before  making  a  definite  statement  as  to  the  strength  of  the 
muscles  it  is  well  to  have  the  candidate  return  several  times,  for,  as 
has  been  said,  practice  and  knack  play  a  great  part  in  this  examina- 
tion. Always  test  the  divergence  first,  then  the  sursumvergence,  and 
finally  the  convergence. 

MUSCLES. 

If  there  is  a  marked  imbalance  of  the  ocular  muscles,  it  will  be  well 
to  use  a  black  wall  as  a  tangent  screen  and  make  a  record  of  the 
diplopia  in  the  various  fields  as  obtained  by  the  use  of  the  ruby  glass 
and  light  at  a  distance  of  30  inches  from  the  wall.  This  should  be 
recorded  on  the  tangent  screen  charts  which  have  been  provided  and 
filed  with  the  5  by  8  history  card. 

ACCOMMODATION    (NEAR  POINT). 

The  near  point  accommodation  is  measured  by  means  of  the  Prince 
rule,  using  the  type  Jaeger  No.  1,  or  the  Duane  disk,  as  the  test  object. 
The  Prince  rule  has  been  gouged  out  at  one  end  to  permit  its  use  in 
the  midline,  as  in  this  way  it  can  be  placed  over  the  nose,  in  contact 
with  an  ink  mark  which  is  12  millimeters  in  front  of  the  cornea. 
This  point  is  measured  by  placing  a  millimeter  rule  alongside  the 
forehead  and,  with  the  gaze  fixed  straight  ahead,  12  millimeters  are 
measured  off.  The  point  thus  determined  is  marked  on  the  nose. 
The  test  object  is  brought  slowly  toward  the  eye  until  the  first  sign 
of  blurring  is  noted.  This  procedure  is  repeated  several  times,  in- 
structing the  candidate  to  exert  all  his  power  so  that  the  test  object 


148 


1 


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3  3 


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149 


MANUAL   OF   MEDICAL  RESEARCH    LABORATORY.  149 

may  be  brought  as  close  to  the  eye  as  possible,  for  we  know  that  the 
first  contraction  of  a  muscle  is  seldom  its  strongest.  The  reading  at 
which  the  test  object  was  brought  closest  to  the  eye  is  recorded  in  milli- 
meters. It  is  well  to  have  a  good  light  from  a  75-watt  nitrogen  day- 
light lamp  shining  directly  on  the  type,  and  the  test  is  more  accurate 
if  the  test  type  is  held  slightly  below  the  horizontal  plane. 

PUPILLARY   DIAMETER. 

With  the  candidate  seated  in  the  chair  in  which  he  is  to  be  tested, 
and  with  the  same  light  that  will  be  used  later  on,  he  is  asked  to  fix 
a  distant  object.  A  millimeter  rule  is  inverted  above  the  pupil  with 
a  plus  2.75  sph.  superimposed,  and  the  reading  is  made  while  looking 
through  the  lens.  If  greater  accuracy  is  desired,  a  pupillometer 

should  be  used. 

COLOE  VISION. 

For  this  purpose  Jenning's  color  test  is  used.  The  method  of 
making  the  test :  The  cover  of  the  green  side  of  the  box  is  removed, 
the  color  board  is  lifted  out,  a  record  sheet  inserted,  and  the  color 
board  replaced.  In  replacing  the  color  board  CARE  MUST  BE 
TAKEN  TO  SEE  THAT  ITS  TOP,  MARKED  ON  THE  BACK 
"NO.  1  GREEN,"  CORRESPONDS  TO  THE  TOP  OF  THE 
RECORD  SHEET.  The  box  is  now  turned  around  several  times 
until  all  sense  of  direction  is  lost.  The  green  test  skein,  fastened 
to  the  inside  of  the  box  lid,  is  placed  at  a  distance  of  2  feet  and 
the  candidate  is  given  the  stylus  and  requested  to  look  along  each 
row  of  colored  patches  and  when  he  sees  the  test  color,  or  one  of 
its  lighter  or  darker  shades,  he  is  to  place  the  point  of  the  stylus  in 
the  opening  and  punch  a  hole  in  the  paper  beneath.  Have  him 
understand  that  he  is  not  expected  to  find  an  exact  match  for  the 
test  skein  but  that  he  is  to  indicate  all  the  color  patches  that  appear 
to  him  to  be  same  general  color  as  the  test  skein,  both  those  that  are 
lighter  and  those  that  are  darker  in  shade.  Having  completed  Test 
No.  1,  the  record  sheet  is  removed,  the  cover  is  replaced,  and  the  box 
turned  over,  exposing  Test  No.  2,  the  ROSE.  The  same  record  sheet 
is  placed  under  the  rose  color  board,  CARE  BEING  TAKEN  TO 
HAVE  THE  TOP  OF  THE  RECORD  SHEET  AND  THE  TOP 
OF  THE  COLOR  BOARD,  MARKED  ON  THE  BACK  "NO. 
2  ROSE,"  correspond.  The  rose  test  skein  is  now  displayed  and 
the  test  proceeds  as  before.  If  the  candidate  seems  to  have  been 
uncertain  in  the  selection  of  colors  or  you  suspect  that  he  may  have 
been  coached  in  the  test,  turn  the  card  with  the  colored  wools  and 
the  blank  on  the  reverse  side  and  have  another  reading  made.  An- 


150  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

other  way  to  confuse  the  subject  is  to  cut  a  circle  in  a  piece  of  paper 
and  place  it  over  the  peripheral  skeins. 

REACTION    OF    THE    IRIS    TO    LIGHT    AND    ACCOMMODATION. 

The  reaction  of  the  iris  to  direct  and  indirect  light  and  accom- 
modation is  noted  and  recorded  as  plus  (meaning  reacts)  1,  2,  and  3, 
being  increased  reaction,  minus  1,  2,  and  3  meaning  degrees  of  slug- 
gish reaction,  and  0  no  reaction.  The  reaction  to  accommodation  is 
determined  by  requiring  the  candidate  to  look  in  the  distance  and 
then  fix  on  a  2-millimeter  black  dot  on  a  white  card  held  10  centi- 
meters in  front  of  the  eye.  The  reaction  to  light  is  best  taken  in  a 
dark  room,  requiring  the  candidate  to  look  into  the  distance  and 
directing  light  from  the  Hare-Marple  ophthalmoscopic  mirror  through 
the  pupil  and  noting  the  reaction  in  both  eyes.  It  may  be  taken 
more  roughly,  with  the  candidate  facing  a  window  and  fixing  a  dis- 
tant object,  both  eyes  being  covered;  the  covers  are  removed  alter- 
nately and  the  reaction  to  direct  and  indirect  light  noted. 


NEAR  POINT  OF  CONVERGENCE. 


The  Prince  rule  and  a  2-millimeter  black  dot  as  a  test  object  are 
used.  The  end  of  the  rule  rests  across  the  bridge  of  the  nose  at  a 
point  12  millimeters  in  front  of  the  cornea.  The  test  object  is 
brought  slowly  toward  the  eyes  slightly  below  the  horizontal  plane 
until  there  is  a  doubling  of  the  dot  or  one  or  both  of  the  candidate's 
eyes  ceases  to  fix.  The  test  is  repeated  several  times,  instructing  the 
candidate  to  exert  his  maximum  effort,  and  the  reading  which  was 
closest  to  the  eye  is  recorded. 

STEREOSCOPIC    VISION. 

An  ordinary  stereoscope  and  the  A,  B,  and  C  cards  are  furnished. 
The  stereoscope  should  be  held  away  from  the  candidate's  eyes  and 
gradually  brought  up  to  them,  instructing  him  that  he  is  to  look  at 
the  pictures  just  as  he  would  look  at  objects  in  a  show  case  in  a  store 
window.  He  is  then  asked  to  move  the  card  backward  and  forward 
until  the  point  is  reached  at  which  the  pictures  are  most  distinct,  and 
his  eyes  are  most  comfortable.  He  is  then  asked  to  name  the  objects 
by  number  as  he  sees  them,  from  before  backward.  The  usual  order 
with  the  A  card  is  9-1-7,  3-2-4,  5-6-8,  and  10.  Confusion  of  4  and  5, 
9  and  1,  and  8  and  10  is  permissible.  To  further  test  the  candidate 
on  the  same  card,  he  may  be  asked  to  name  the  smaller  objects  on 
No.  9,  from  before  backwards,  they  are  cross,  balloon,  and  flag.  On 
No.  8,  balloon,  cross,  rod,  and  pennant.  No.  10,  pennant,  balloon, 
and  cross.  The  usual  order  for  the  B  card  is  7-5-9,  3-4-2,  1-10-8. 
and  6;  for  the  C  card,  10-9-2,  7-8-6,  4-3-1,  and  5. 


MHC  Jun«1/(8 


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150-2 


150-3 


151-1 


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151-2 


MANUAL  OF   MEDICAL  BESEAKCH   LABOEATOEY.  151 

OPHTHALMOSCOPIC    EXAMINATION. 

The  direct  and  indirect  methods  should  be  used,  noting  any 
changes  in  the  lens,  media,  or  fundus. 

PRELIMINARY  REPORT  or  THE  RESEARCH  WORK  OF  THE  OPHTHALMO- 
LOGICAL  DEPARTMENT,  MEDICAL  RESEARCH  LABORATORY,  JULY  IT, 
1918. 

Although  the  number  of  men  examined  has  been  few  and  the 
research  work  carried  out  under  adverse  conditions,  an  outline  of 
the  results  so  far  accomplished  may  prove  of  some  value  in  helping 
us  care  for  the  flier  in  a  more  scientific  manner. 

The  most  important  problem  is  the  one  of  visual  acuity,  and  it  is 
absolutely  essential  that  the  pilot  or  observer  have  as  nearly  perfect 
vision  as  nature  permits  under  normal  conditions,  and  furthermore 
that  the  visual  acuity  will  not  show  a  marked  deterioration  due  to 
the  lack  of  oxygen. 

Visual  acuity  has  been  studied  using  Ives'  test  object  and  John- 
son's visual  acuity  test  apparatus  and  also  with  the  ordinary  Snellen 
test  type.  The  Ives'  visual  acuity  test  object  has  been  found  to  be 
of  the  greatest  value  for  taking  the  visual  acuity  on  the  rebreathing 
apparatus,  due  to  the  fact  that  the  subject  could  raise  his  hand  when 
he  first  perceived  the  lines.  In  the  low-pressure  chamber  it  has  also 
proven  of  value,  for  the  first  surface  mirror  could  be  used  to  increase 
the  reading  distance. 

Forty-four  subjects  were  examined  on  the  rebreathing  apparatus 
and  in  the  low-pressure  chamber.  They  were  classified  as  normal 
and  subnormal;  i.  e.,  those  who  could  pass  the  examination  for  the 
Department  of  Military  Aeronautics  and  those  who  would  be  ocu- 
larly disqualified.  The  13-,  subnormal  subjects  were  so  classified  be- 
cause of  defective  vision  arising  from  errors  of  refraction. 


Normal. 

Subnormal. 

Vision  improved  .  . 

3  (10  per  cent)  

Vision  decreased  

8  (26  per  cent)  

5  (38.5  per  cent). 

No  change  

20  (64  per  cent).. 

8  (61.5  pei  cent)  . 

One  of  the  French  observers  claimed  that  the  visual  acuity  in- 
creases at  an  altitude  of  2,000  meters  and  that  this  was  probably  due 
to  congestion  of  the  head  and  in  particular  of  the  choroid  and  retina. 
Normal  visual  acuity  readings  were  taken,  using  the  Johnson  appa- 
ratus, then  a  three-minim  pearl  of  amyl  nitrite  was  inhaled  to  pro- 
duce congestion.  Twelve  men  were  examined  and  there  was  im- 
pairment of  vision  during  the  period  of  maximum  nitrite  effect  in  all 
except  one,  a  myope.  During  the  first  stage  of  the  action  of  the  drug 
there  was  a  slight  increase  in  visual  acuity  in  most  instances. 


152  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

The  effect  of  tobacco  upon  the  visual  acuity  has  also  been  studied. 
Smoking  one  strong  cigar  or  inhaling  one  or  two  cigarettes,  controls 
were  made  in  most  instances.  Twelve  or  75  per  cent  showed  falling 
off  in  visual  acuity  over  the  control,  6  per  cent  showed  a  rise,  and 
three,  or  19  per  cent,  showed  no  change.  This  subject  will  be  taken 
up  in  full  under  the  effects  of  tobacco  on  the  eye. 

REACTION  TIME. 

The  French  and  Italians  have  laid  great  stress  upon  the  determina- 
tion of  the  reaction  time,  and  it  is  undoubtedly  important  that  the 
pilot  or  observer  act  and  think  a  little  more  rapidly  than  his  adver- 
sary, if  he  is  to  have  the  advantage.  All  the  men  who  have  done  the 
most  work  in  reaction  time  in  this  country  believe  that  some  form  of 
complex  reaction  time  will  prove  of  value,  but  they  are  skeptical  as  to 
the  results  obtained  with  the  simple  reaction  time  tests  employed  by 
the  French  and  Italians.  With  this  in  mind  the  -  -  visual  dis- 
crimination reaction  time  experiment  with  four  possible  correct  reac- 
tions and  five  possible  stimuli  has  been  chosen.  The  subject  presses 
the  telegraphic  key  the  moment  the  stimulus  appears  upon  the  ground- 
glass  plate.  The chronoscope  starts  recording  time  the 

moment  the  light  appears  on  the  ground  glass  and  is  stopped  by  the 
subject's  reaction.  The  chronoscope  records  time  in  0.12  of  a  second 
and  the  average  discrimination  reaction  of  a  normal  subject  is  ap- 
proximately one-half  second,  and  for  simple  reaction  time  one-fifth 
of  a  second. 

JUDGMENT  OF  DISTANCE  AND  STEREOSCOPIC  VISION. 

There  are  many  factors  involved  in  the  judgment  of  distance,  but 
undoubtedly  stereopsis  is  of  importance  in  the  accurate  performance 
of  this  complex  act  and  therefore  it  has  been  considered  important 
that  the  stereoscopic  vision  be  tested  under  conditions  of  low-oxygen 
tension. 

The  stereoscopic  vision  was  tested  on  the  rebreather  and  in  the 
low-pressure  chamber  by  use  of  the  ordinary  stereoscope  containing 
7-degree  prisms,  base  out,  with  a  plus  5.50  sphere  superimposed. 
The  ability  to  maintain  perfect  stereopsis  at  high  altitudes  was 
noted. 

Nineteen  normal  subjects  were  examined  on  the  rebreather  with  a 
loss  of  stereopsis  in  only  three  of  them,  or  15.7  per  cent.  Readings 
were  taken  at  six-minute  intervals  throughout  the  run.  Of  seven 
men  ocularly  disqualified  stereopsis  was  lost  in  only  one.  In  no 
case  was  a  change  noted  below  20,000  feet. 

Seven  "normals"  and  nine  "subnormals"  were  examined  in  the 
low-pressure  chamber.  Here  readings  were  taken  at  10,000,  15,000, 


MANUAL  OE   MEDICAL  RESEARCH   LABORATORY.  153 

and  20,000  feet.  All  seven  normals  remained  unchanged  and  only 
one  subnormal  showed  any  confusion  in  stereopsis.  This  change 
was  noted  at  15,000  feet,  but  normal  stereopsis  was  promptly  re- 
stored by  the  administration  of  oxygen. 

COLOR  VISION. 

Color  vision  is  considered  important  for  the  flier  by  most  of  the 
allied  nations,  and  certainly  it  plays  an  important  role  in  judging 
the  color  of  fields  and  swamps  in  landing.  To  accurately  determine 
the  color  of  roofs,  chimneys,  lights,  etc.,  particularly  colored  lights 
at  night,  good  color  vision  is  surely  necessary.  We  have  endeavored 
to  determine  the  effect  of  lowr-oxygen  tension  upon  color  vision. 
Stillings  plates  were  used  in  these  tests.  Five  subjects  were  carried 
to  20,000  feet  or  over  in  the  low-pressure  chamber  and  five  above 
20,000  feet  on  the  rebreathing  apparatus.  There  was  no  change  in 
color  vision  during  these  tests. 

FIELD  OF  BINOCULAR  SINGLE  VISION  AND  FIELD  OF  BINOCULAR  FIXATION. 

The  field  of  binocular  single  vision  has  been  tested  by  means  of 
a  tangent  screen.  The  field  of  binocular  fixation  has  been  tested 
by  the  use  of  the  modified  Schweiger  perimeter  and  small  dots  on  a 
white  card.  One  hundred  and  twenty-two  men  with  normal  eyes 
were  examined  and  16  who  were  ocularly  subnormal.  Seven  and 
thirty-seven  one-hundredths  per  cent  of  the  normals  showed  contrac- 
tion of  the  field  of  binocular  fixation.  Fifty  per  cent  of  the  subnor- 
mals showed  this  contraction.  Contraction  of  the  field  was  more 
marked  above. 

MUSCLE  BALANCE  AND  MUSCLE  STRENGTH. 

It  is  important  for  the  flier  that  his  muscle  balance  be  as  nearly 
normal  as  possible,  for  small  defects  are  accentuated  by  the  strain  of 
flying  and  lack  of  oxygen,  resulting  in  a  marked  contraction  of  the 
field  of  binocular  single  vision,  and  sometimes  diplopia  is  produced, 
even  at  low  altitudes.  Research  work  has  demonstrated  that  exo- 
phoria  and  hyperphoria  are  more  objectionable  than  esophoria. 

To  determine  the  effect  of  lack  of  oxygen  upon  the  ocular  muscles 
35  men,  acceptable  for  the  Air  Service,  have  been  examined  on 
the  rebreathing  apparatus  and  the  findings  checked  by  repeating 
the  test  in  the  low-pressure  chamber.  The  muscle  duction  was 
taken  at  sea  level,  5,000,  10,000,  15,000,  and  20,000  feet,  and  at 
this  point  oxygen  was  given  in  the  low-pressure  chamber  for  five 
minutes,  and  on  the  rebreathing  apparatus  the  mouthpiece  was  taken 
out,  allowing  the  subject  to  breathe  normally.  Oxygen  or  breathing 


154 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


atmospheric  air  caused  a  return  of  the  muscle  strength  to  normal  in 
from  three  to  five  minutes.  The  general  averages  of  the  strength  of 
the  muscles  at  sea  level  is  as  follows : 


Superduction. 
2.8°^ 

Abduction. 
6.2° 

Adduction. 
16.8° 

Loss  of  strength  during  the  rebreathing  test: 
15,000  feet  or  11.8  per  cent  oxygen  

0      P.  ct. 
1.  1      (39) 

°      P.  ct. 

1.  5      (24) 

P.  ct. 
1.  8    (9.  5) 

20,000  feet  or  9.7  per  cent  oxygen.  . 

1.  9      (70) 

1  83    (29) 

2  94     (17) 

Loss  of  strength  during  low  pressure  chamber  test: 
15,000  feet  or  11.8  per  cent  oxygen  

1.  05    (37) 

1.  35    (21) 

1.75    (10) 

20,000  feet  or  9.7  per  cent  oxygen  

1.  7      (64) 

1.8      (29) 

2.8      (16) 

In  all  the  subnormal  subjects  examined,  particularly  those  with 
convergence  insufficiency  alone  or  combined  with  divergence  excess, 
there  was  a  marked  loss^in  the  power  of  adduction,  and  diplopia 
often  occurred  between  10,000  and  15,000  feet.  Men  with  over  one 
degree  of  hyperphoria,  particularly  when  combined  with  exophoria, 
showed  a  rapid  reduction  in  muscle  strength,  often  resulting  in 
diplopia.  Subjects  in  the  subnormal  group  should  be  cared  for  by 
muscle  exercises  and  operations  where  it  is  found  necessary. 

FIELD  OF  VISION. 

• 

It  is  of  the  utmost  importance  that  the  aviator  have  the  broadest 
possible  field  of  vision,  for  we  know  that  the  visual  field  is  contracted 
slightly,  due  to  the  lack  of  oxygen,  and  that  marked  constriction  of 
the  field  is  produced  by  poorly  constructed  goggles  as  well  as  by  blind 
angles  in  aeroplane  construction.  The  fields  for  form  and  color  have 
been  taken  in  the  low-pressure  chamber  at  5,000,  10,000,  15,000,  and 
20,000  feet,  and  when  contraction  is  noted  at  20,000  feet  oxygen  is 
administered.  To  make  sure  that  the  changes  are  not  due  to  fatigue, 
controls  have  been  taken  at  sea  level,  corresponding  in  time  of  day 
and  in  time  interval  to  those  taken  in  the  low-pressure  chamber.  At 
5,000  and  10,000  feet  there  is  usually  a  slight  enlargement  of  the 
fields  for  form  and  color,  at  15,000  feet  a  slight  contraction,  and  at 
20,000  feet  a  marked  contraction.  Twenty  men  have  been  examined, 
and  at  20,000  feet  the  fields  for  form  have  shown  a  contraction  of  14 
per  cent  of  their  original  size  below,  3.5  per  cent  in  the  temporal 
field,  4  per  cent  above,  and  6  per  cent  nasally.  The  green,  4.5  per 
cent  in  the  lower,  5  per  cent  in  the  temporal,  5  per  cent  above,  and  25 
per  cent  in  the  nasal  field.  Five  minutes  after  returning  to  sea  level 
fields  are  normal  in  size.  Giving  oxygen  at  20,000  feet  for  four  or 
five  minutes  caused  a  return  of  the  fields  to  normal.  Several  fields 
have  been  taken  on  the  rebreathing  apparatus,  and  the  results  are 
fairly  comparable  with  those  found  in  the  low-pressure  chamber. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  155 

PERCEPTION   OF   MOTION   BY  THE  RETINA. 

It  is  important  that  the  aviator  note  the  approach  of  an  enemy 
plane  before  the  enemy  sees  him,  and  therefore  the  keen  sense  of 
perception  of  motion  by  the  retina  is  a  valuable  asset  to  the  flier.  It 
has  been  our  endeavor  to  provide  some  method  of  taking  and  record: 
ing  these  fields  in  the  hope  that  something  of  practical  value  might 
be  found. 

These  fields  were  taken  in  a  dark  room  with  no  illumination  other 
than  that  of  the  test  object,  for  which  purposes  a  May  ophthalmoscope 
battery  handle  with  the  cap  removed  was  used. 

The  subject  was  seated  at  a  distance  of  15  inches  from  the  center 
of  the  screen.  The  test  object  was  held  on  the  opposite  side 
of  the  screen  from  the  object  and  gradually  moved  until  it  came  into 
the  field  of  vision.  In  this  manner  the  pla'ce  at  which  the  motion  of 
the  light  could  be  first  seen  was  noted,  and  then  at  what  point  the 
correct  perception  of  direction  of  motion  could  be  ascertained.  Lastly, 
the  field  of  form  was  taken,  i.  e.,  the  first  point  at  which  the  stationary 
light  could  be  recognized. 

The  relative  sizes  of  these  three  fields  can  be  seen  by  the  average 
figures  of  10  cases : 


Field  of 
motion. 

Field  of 
direction 
of  motion. 

Field  of 
form. 

Up...                                      

33 

31* 

29* 

Down  

47J 

45 

42J 

Right  

45 

42 

40 

Left  

47 

43 

42f 

Up  and  right  ...                           

42 

40 

35 

Up  and  left.          .  .        ..          

41 

38 

36 

Down  and  right 

48 

45 

43 

Down  and  left                                                                                             .  . 

47 

44 

43 

The  field  of  motion  is  approximately  3  degrees  larger  than  the 
field  of  direction  of  motion,  which,  in  turn,  is  about  1£  degrees 
larger  than  that  of  form.  It  is  evident,  then,  that  a  moving  object' 
can  be  seen  4r|  degrees  sooner  than  a  stationary  one.  That  is,  the 
field  of  motion  is  4^  degrees  larger  in  every  direction  than  that  of 
form.  This  relationship  is  apparently  a  constant  one,  independent 
of  the  size  of  the  field.  In  other  words,  if  motion  is  perceived  at  a 
certain  point,  you  expect  to  find  the  perception  of  form  4|  degrees 
farther  in  toward  the  center.  In  a  like  manner  the  field  of  percep- 
tion of  direction  of  motion  bears  a  rather  constant  relationship  to 
that  of  motion  and  of  form. 

INTRAOCULAR  TENSION. 

Intraocular  tension  has  been  studied  in  the  low-pressure  chamber. 
Fourteen  men  have  been  examined  in  the  low-pressure  chamber. 
No  correlation  has  been  found,  either  between  intraocular  tension 


156  MANUAL  OF   MEDICAL   RESEARCH    LABORATORY. 

and  the  blood  pressure  or  lowered  oxygen  tension  and  various  cardio- 
vascular changes,  for  the  intraocular  tension  has  sometimes  gone  up 
as  the  barometric  pressure  was  lowered  and  sometimes  it  has  gone 
down  with  the  lowering  of  barometric  pressure.  This  also  holds 
true  for  the  blood  pressure.  However,  before  definite  conclusions 
should  be  made  more  work  should  be  done. 

ACCOMMODATION. 

The  flier  must  continually  observe  the  instruments  on  the  inside 
of  the  fuselage,  particularly  at  night,  and  therefore  it  is  important 
that  the  accommodation  should  not  fall  off  too  rapidly,  due  to  lack 
of  oxygen.  The  rule  of  accommodation  in  visual  acuity  and  in 
judgment  of  distance  is  also  important. 

The  near  point  of  accommodation  has  been  taken  every  two  min- 
utes in  the  low-pressure  chamber  and  on  the  rebreathing  apparatus, 
using  a  Prince  rule  with  Jaeger  test  type  or  the  Duane  disk  as  a 
test  object.  Normal  runs  have  been  made  without  the  low  oxygen 
tension  effect  for  the  purpose  of  comparison.  One  hundred  and 
forty-eight  men,  acceptable  for  the  Aviation  Service  as  fliers,  were 
examined  on  the  rebreathing  apparatus;  44.6  per  cent  showed  a 
receding  of  the  near  point,  18  per  cent  showed  improvement,  fluctu- 
ating changes  in  accommodation  were  noticed  in  14.4  per  cent,  and 
no  change  in  23  per  cent.  Eleven  subnormal  cases  were  examined, 
and  63.7  per  cent  manifested  a  decrease  in  accommodative  power, 
18.3  per  cent  an  apparent  increase,  9  per  cent  showed  no  change,  and 
9  per  cent  variable  reactions.  The  low  pressure  chamber  findings 
were  practically  the  same  as  those  with  the  rebreather.  Of  17 
normal  men  examined,  47  per  cent  showed  decrease  in  accom- 
modative power,  11.7  per  cent  increase,  23  per  cent  fluctuation,  and 
7.8  per  cent  no  change.  Three  subnormal  subjects  were  examined  in 
the  low-pressure  chamber;  two  showed  a  decrease  in  accommodative 
power  and  the  other  gave  a  varying  reaction.  When  the  subject  is 
brought  to  sea  level  the  accommodation  comes  back  rapidly  in  some 
and  slowly  in  others.  The  inhalation  of  oxygen  invariably  causes  a 
return  to  normal,  even  though  the  subject  may  be  kept  at  20,000  feet 
in  the  low-pressure  chamber. 

That  these  changes  do  not  follow  the  cardio-vascular  reactions  is 
shown  by  the  fact  that  57  men,  exhibiting  acceleration  of  pulse  rate 
and  maintenance  of  pulse  pressure,  showed  in  42.1  per  cent  decrease 
in  the  power  of  accommodation,  15.8  per  cent  increase  in  power  of 
accommodation,  15.8  per  cent  fluctuation  in  accommodation,  and  26.3 
per  cent  no  change  in  accommodation.  Our  researches  would  lead  us 
to  believe  that  hyperopes  and  subjects  with  a  marked  amount  of 
hyperopic  astigmatism  show  the  most  marked  changes  in  accommo- 
dation. 


MANUAL   OF    MEDICAL  RESEARCH   LABORATORY.  157 

Fatigue  of  accommodation  has  been  studied  with  an  ophthalmic 
ergograph.  Normal  three-minute  runs  were  made  without  the  low 
oxygen  tension  effect  as  controls,  then  three-minute  runs  with  same 
time  interval  were  made  in  the  low-pressure  chamber  and  on  the 
rebreathing  apparatus.  The  findings  on  the  rebreathing  apparatus 
and  in  the  low-pressure  chamber  showed,  at  15,000  feet,  a  more  rapid 
onset  of  fatigue 'than  was  evidenced  by  the  controls,  and  at  20,000 
feet  the  fatigue  was  marked.  The  administration  of  artificial  oxygen 
rapidly  restored  the  normal  tone  of  the  ciliary  muscle. 


CONVERGENCE. 


If  the  near  point  of  convergence  falls  off  markedly  during  flying, 
the  aviator's  ability  to  make  landings  properly  will  be  impaired,  and, 
therefore,  the  near  point  of  convergence  has  been  taken  during  the 
rebreathing  test  and  low-pressure  chamber  experiment. 

A  U-shaped  piece  was  cut  out  of  the  Prince  rule  to  fit  over  the 
nose  and  a  2-millimeter  black  dot  on  a  white  background  was  used  as 
a  test  object  for  making  this  determination.  Readings  were  taken 
without  low-oxygen  tension  effect,  with  low-oxygen  tension  effect,  and 
the  effect  of  the  administration  of  oxygen  was  determined.  Read- 
ings were  taken  every  two  minutes  and  charted.  One  hundred  and 
forty-seven  men  with  normal  eyes  were  examined  on  the  rebreathing 
apparatus. 

50.3  per  cent  decrease  in  convergence  power. 
17.6  per  cent  increase  in  convergence  power. 

11.5  per  cent  fluctuation  in  convergence  power. 

20.6  per  cent  no  change  in  convergence  power. 

Of  11  subnormal  men  examined  6  were  disqualified  for  visual  acuity 
and  5  for  muscular  imbalance ;  45.7  per  cent  showed  decrease  in  power 
of  convergence.  Increased  converging  power,  fluctuating  changes, 
and  no  change  in  the  near  point  of  convergence  were  each  noted  in 
18.1  per  cent.  Of  16  normal  men  examined  in  the  low-pressure  cham- 
ber 50  per  cent  showed  falling  off  in  power  of  convergence,  none 
showed  increase,  fluctuating  reactions  were  present  in  12.5  per  cent, 
and  37.5  per  cent  remained  unchanged.  In  the  subnormal  group 
the  recession  of  the  near  point  of  convergence  was  very  marked, 
sometimes  resulting  in  diplopia. 

An  attempt  has  been  made  to  show  what  relationship,  if  any, 
exists  between  the  convergence  and  the  cardio-vascular  reactions  to 
low-oxygen  tension. 

Seventy-two  cases  showing  an  increase  in  pulse  rate  and  a  main- 
tenance in  pulse  pressure  gave  these  convergence  changes,  which 


158  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

would  seem  to  indicate  that  ocular  changes  can  not  be  predicted  by 
the  cardio- vascular  reaction  and  vice  versa. 

54.2  per  cent  decrease  in  power  of  convergence. 

15.3  per  cent  increase  in  power  of  convergence. 
9.7  per  cent  fluctuation  in  power  of  convergence. 

20.8  per  cent  no  change  in  power  of  convergence. 

The  results  would  indicate  that  the  rebreathing  apparatus  and 
low-pressure  tank  give  almost  identical  findings,  and  in  each  case 
the  determining  factor  seems  to  be  the  lowering  of  oxygen  tension 
as  the  administration  of  oxygen  soon  causes  the  convergence  near 
point  to  return  to  normal,  irrespective  of  the  barometric  pressure. 

Fatigue  of  convergence  has  been  studied  with  Howe's  ophthalmic 
ergograph.  Normal  3-minute  runs  as  controls  were  made  without 
the  low  oxygen  tension  effect,  then  3-minute  Buns  with  approximately 
the  same  time  interval  were  made  in  the  low-pressure  chamber  and 
on  the  rebreathing  apparatus.  The  findings  on  the  rebreathing 
apparatus  and  in  the  low-pressure  chamber  showed  a  more  rapid 
onset  of  fatigue  than  occurred  with  the  controls.  At  15,000  feet  and 
at  20,000  feet  the  fatigue  was  marked,  as  was  the  case  with  accom- 
modation. Here  also  the  administration  of  oxygen  caused  a  rapid 
return  of  converging  power. 

RETINAL   SENSITIVITY. 

The  Italians  have  laid  considerable  stress  upon  retinal  sensitivity 

for  those  men  who  must  fly  at  night,  and  Lieut.  has  devised 

a  test  for  the  contrast  sensitivity  of  the  retina  which  has  proven 
most  useful  and  practical. 

It  is  important  that  the  retina  be  normally  sensitive  to  light  im- 
pressions, especially  for  those  men  who  must  fly  at  night,  notably 
bombers  and  fliers  doing  patrol  duty.  A  test  for  the  contrast  sen- 
sitivity of  the  retina  has  proven  most  practical  for  our  work,  and 
only  men  who  have  normal  sensitivity  in  this  respect  will  be  selected 
for  night  flying. 

In  this  laboratory  tests  to  determine  the  threshold  sensitivity  for 
white  and  colored  lights  and  for  contrast  are  conducted  in  the  follow- 
ing manner : 

The wedge  is  made  of  two  pieces  of  glass  at  a  known  angle, 

between  which  is  run  a  solution  of  gelatine  and  neutral  dye.  The 
wedge  is  calibrated  in  millimeters,  which  is  translatable  into  per 
cent  of  light  transmitted. 

To  test  the  threshold  sensitivity  to  light  the  subject  is  placed  20 
feet  from  a  spot  of  light  3  millimeters  in  diameter.  Holding  the 
wedge  before  the  right  eye,  he  slowly  draws  the  slide  from  its  cover, 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  159 

and  as  the  light  just  disappears  a  reading  is  taken.  This  reading 
is  in  millimeters  and  is  then  translated  to  per  cent  transmission. 

The  threshold  for  color  is  taken  the  same  as  the  above,  using  red 
and  green  light,  which  are  practically  monochromatic. 

The  test  of  contrast  sensitivity  is  made  with  a  -  wedge  and 

-  contrast  square.  The  contrast  square  is  made  by  placing  a 
square  of  dark  gray  paper  upon  a  larger  square  of  lighter  gray,  there 
being  13  perceptible  differences  between  the  two  shades.  An  illit- 
erate "  E  "  with  the  same  perceptible  differences  is  used  as  a  check  of 
the  findings.  This  is  lighted  by  a  75-watt  nitrogen  daylight  lamp  at 
a  given  angle  and  distance  from  the  test  object  and  the  subject  is 
placed  20  feet  in  front  of  the  object.  The  reading  on  the  wedge  is 
taken  just  as  the  contrast  between  the  squares  disappears.  The  aver- 
age readings  taken  with  the  contrast  sensitivity  square  give  34  milli- 
meters and  the  illiterate  "  E  "  32  millimeters.  To  date,  the  normal 
for  the  light  threshold  of  35  cases  is  65  millimeters. 

Under  the  rebreathing  test  the  threshold  for  light  has  shown  au 
improvement  in  25.9  per  cent;  44.5  per  cent  show  neither  improve- 
ment nor  falling  off;  and  29.6  per  cent  show  a  falling  off  in  sensi- 
tivity. 

In  the  study  of  the  threshold  for  colors  the  red  and  green  both 
show  a  falling  off  in  71.4:  per  cent  and  neither  a  gain  or  loss  in  26.6 
per  cent. 

In  former  tests  with  a  blue  light,  which  was  not  absolutely  mono- 
chromatic, there  was  improvement  in  66.6  per  cent  and  falling  off  in 
33.4  per  cent. 

ACCOMMODATION  TEST/OBJECT. 

It  has  been  important  for  our  work  to  determine  the  best  possible 
test  object  for  determining  the  near  point  of  accommodation. 

The  object  of  these  tests  is  to  determine  the  comparative  value  of 
various  test  objects  used  in  determining  the  near  point  of  accommo- 
dation. Tests  were  also  made  to  determine  the  difference,  if  any, 
between  a  black  and  white  dot  in  determining  the  near  point  of  con- 
vergence. The  objects  used  in  these  tests  were  as  follows: 

1.  Radiating  squares.  4.  Jaeger  type,  No.  1. 

2.  Illiterate  "  E."  o.  Duane  disk. 

3.  Numbers.  6  Prince  rule. 

Two  separate  examinations  were  made  for  each  test  object. 
Twenty-five  men  were  examined,  and  a  general  average  gave  the  fol- 
lowing results  of  difference  in  readings 

Millimeter. 

Radiating  squares 14^ 

Illiterate  "E" 4£ 

Numbers 5j 

Jaeger,  No.  1 ; 4£ 

Duane  disk 3| 


160  MANUAL   OP   MEDICAL  RESEARCH    LABORATORY. 

The  Duane  disk  is  the  best  test  object  for  general  use.  It  is 
found,  however,  that  during  the  rebreathing  test  it  is  difficult  for 
the  subject  to  quickly  recognize  the  faint  black  line  on  the  disk,  and 
the  later  readings  are  not  satisfactory.  Tests  of  black  and  white 
dots  in  finding  the  near  point  of  convergence  show  no  appreciable 
difference  between  them. 

As  Jaeger  type  is  not  standardized,  and  as  the  various  units  should 
have  some  standard  in  order  to  obtain  uniform  results,  a  plate  has 
been  made  with  two  sizes  of  standard  type.  This  type  is  made  up  of 
mixed  letters  and  numbers.  The  smaller  type  is  0.6  millimeter  and 
the  larger  0.8  milimeter,  so,  should  the  accommodation  fall  off  late 
in  the  tests,  the  larger  type  can  be  seen.  Above  the  letters  is  a  black 
dot  for  use  in  determining  the  near  point  in  convergence,  thus  elim- 
inating a  certain  amount  of  delay  in  changing  cards  during  the  test. 

ASTIGMATISM. 

The  effect  of  lowered  barometric  pressure  and  lack  of  oxygen  upon 
astigmatism  has  been  tested  in  several  instances,  and  so  far  no  change 
has  been  shown  in  astigmatism  due  to  lack  of  oxygen  or  lowered  baro- 
metric pressure. 

EXAMINATION    OF    THE    FUNDUS    DURING    REBREATHING    AND    LOW    PRES- 
SURE  EXPERIMENTS. 

There  has  been  very  little  change  noted  in  the  f  undus'  appearance, 
but  at  the  end  of  the  rebreathing  run  of  above  20,000  feet  in  the  low 
pressure  chamber  the  retinal  vessels  have  shown  some  congestion. 

'% 

IRIS  REACTION   DURING   REBREATHING   AND   LOW  PRESSURE   EXPERIMENTS. 

The  object  of  these  tests  is  to  determine  the  change  in  reactions 
of  the  iris  and  pupillary  diameters  during  rebreathing. 

Fifteen  men  were  examined  for  this  experiment  and  carried  from 
18,000  to  28,000  feet.  The  changes  were  not  altogether  uniform,  as 
certain  of  the  cases  reacted  more  strongly  to  light  than  to  accommo- 
dation, and  vice  versa.  Some  changes,  however,  seem  to  be  fairly 
constant. 

Below  10,000  feet  no  changes  are  noted;  above  this,  varying  in 
different  individuals  as  to  height,  there  is  an  increase  in  reflexes  for 
both  light  and  accommodation.  This  holds  until  late  in  the  experi- 
ment and  then  slowly  diminishes,  and  if  the  subject  is  allowed  to 
remain  on  the  machine  near  fainting  point,  reflexes  are  entirely 
abolished.  The  pupil  slowly  dilates,  usually  beginning  above  15,- 
000  feet  and  remains  so  during  the  remainder  of  the  experiment. 
Tf  allowed  to  remain  on  the  machine  too  near  the  fainting  poinfj 
the  pupil  is  quite  widely  dilated. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  161 

EFFECT  OF  TOBACCO   UPON   THE   EYE. 

The  problem,  as  taken  up  by  the  Ophthalmological  Department 
of  the  Medical  Research  Laboratory,  Hazelhurst  Field,  was  to  deter- 
mine what  effect,  if  any,  tobacco  has  upon  vision,  reaction  time,  reti- 
nal sensitivity,  accommodation,  and  convergence  of  habitues,  and 
nonsmokers.  Although  this  investigation  is  still  uncompleted,  it  is 
believed  that  a  preliminary  report  is  desirable. 

The  widespread,  increasing,  and  unrestricted  use  of  tobacco  in  the 
Army  and  Navy  furnishes  the  practical  incentive  and  justification 
for  the  investigation. 

APPABATTIS  EMPLOYED  THUS  FAB. 

A.  For  visual  acuity:  (1)  Ives  apparatus  at  20  feet.     (2)  Snellen 
test  card.     (Unsatisfactory  and  abandoned  for  this  purpose.) 

NOTE. — 20/20  vision  is  equivalent  to  1.00  on  the  Ives  apparatus. 

B.  For  circulation  effects:  A  standard  sphygmomanometer,  stop 
watch,  and  stethoscope. 

C.  Accommodation  and  convergence    (near  point) :  The  Prince 
rule,  with  Jaeger  test  type,  and  a  2-millimeter  black  dot  on  a  white 
field. 

D.*  Retinal  sensitivity  and  contract  sensitivity:  For  these,  the 
photometric  wedge  was  used,  employed  in  such  a  manner  as  to  blend 
within  a  period  of  5  to  8  seconds,  two  gray  squares,  one  within  the 
other,  differing  from  each  other  in  tint  by  13  perceptible  shades. 
The  squares  must  be  highly  illuminated  by  a  shaded  nitrogen  day- 
light lamp,  and  observed  at  a  distance  of  20  feet. 

TESTS. 

Visual  acuity :  This  was  very  Carefully  taken  on  the  Ives  apparatus 
every  four  minutes  during  smoking,  after  having  previously  taken 
several  preliminary  observations  at  two-minute  intervals.  Where 
possible,  control  tests  lasting  a  half  hour  or  more  were  taken  later 
in  order  to  compare  the  regularity  of  the  curves  with  those  of  the 
tests  while  smoking.  Several  observations  were  made  after  the  sub- 
ject had  ceased  to  smoke. 

In  all  cases  vision  was  taken  separately  for  each  eye,  with  the  sub- 
ject wearing  his  usual  correcting  lenses.  Variation  of  the  direction 
of  the  lines  in  the  Ives  apparatus  was  tried  but  was  discontinued  as 
unsatisfactory  and  the  lines  were  maintained  in  one  position  during 
the  test  (generally  vertical).  This  was  to  avoid  variation  in  read- 
ings due  to  slight  astigmatic  errors. 

Blood  pressure. — This  was  taken  every  four  minutes  after  at  least 
three  preliminary  observations,  two  minutes  apart,  and  was1  con- 
8911&— 18 11 


162  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

tinued  until  the  cigar  was  consumed  with  one  or  more  final  observa- 
tions, two  to  four  minutes  afterwards.  The  systolic  and  diastolic 
pressure  was  taken  by  stethoscope  method. 

Pulse. — Normals  and  test  observations  at  four-minute  intervals. 

Convergence  and  accommodation. — These  were  taken  generally 
every  10  minutes,  as  was  also  retinal  sensitivity  to  contrast. 

Results. — Of  16  subjects  tested  and  their  records  charted  and  curves 
plotted,  results  are  as  follows : 

A.  Visual  acuity:  Twelve  (75  per  cent)  showed  a  fall,  the  average 
of  which  was  0.17  (Ives's  apparatus). 

One  (6  per  cent)  showed  a  rise;  three  (19  per  cent)  not  changed. 

NOTE. — Curves  showing  both  a  rise  and  a  fall  are  classed  accord- 
ing to  which  predominates.  A  slight  preliminary  rise  occurred  in 
nine  cases,  the  dominant  effect  of  which,  however,  was  a  fall.  The 
duration  of  lowered  vision  was  very  brief,  lasting  at  most  only  a  few 
minutes  after  cessation  of  smoking. 

B.  Systolic  and  diastolic  blood  pressure:  Both  were  affected  and 
in  general  similarly,  though  not  in  equal  degree.     Both  showed  a 
rise  of  69  per  cent  in  16  cases.     In  3  (19  per  cent)  there  was  a  fall  of 
the  systolic  and  4  (25  per  cent)  of  the  diastolic  pressure.    The  aver- 
age rise  of  the  systolic  was  9.3  millimeters,  of  the  diastolic  7  milli- 
meters.   The  average  fall  of  the  systolic  was  8  millimeters,  of  the 
diastolic  5.5  millimeters.    Here  also  the  effect  was  temporary,  usu- 
ally lasting  but  a  few  minutes. 

C.  Pulse :  A  rise  in  pulse  rate  was  nearly  constant,  14  cases  out  of 
16  (87£  per  cent)  showing  an  increase,  the  average  of  which  was  14.3 
beats  per  minute.    Two  cases  showed  a  fall  averaging  five  beats. 

D.  Accommodation:  Of  13  subjects,  5  (38  per  cent)  showed  a  loss, 
this  loss  averaging  33  millimeters.     Two  showed  an  improvement 
averaging  12  millimeters;  6  (46  per  cent)  showed  no  change.     Those 
showing  the  greatest  loss  were  presbyopic. 

E.  Convergence:  Of  12  cases,  50  per  cent  showed  more  or  less 
falling  off;  5    (42  per  cent)   showed  no  change.     One  apparently 
improved  by  10  millimeters.    It  will  be  seen  that  the  effect  upon 
convergence  and  accommodation  was  much  more  uncertain  than  in 
the  cases  of  visual  acuity  and  blood  pressure..    The  same  may  be 
said  for  superduction  and  adduction  as  tested  by  prisms. 

F.  Ketinal  contrastivity :  The  use  of  the wedge  elicited  no 

changes  under  tobacco,  so  far  as  could  be  ascertained,  except  in  two 
cases,  which  showed  a  loss  of  10  millimeters. 

Conclusions:  Observations  to  date  indicate  that  approximately  75 
per  cent  of  smokers  have  definite  though  temporary  effects  upon 
vision  from  a  single  cigar,  and  almost  an  equal  proportion  show  a 
rise  in  blood  pressure,  while  there  is  an  increased  pulse  rate  in  nearly 


MANUAL  OF   MEDICAL  EESEAKCH   LABORATORY.  163 

90  per  cent.  This  effect  is  also  temporary,  although  John,  in  1913, 
reported  that  the  use  of  two  cigars  caused  a  rise  of  blood  pressure 
lasting  for  two  hours  after  the  cessation  of  smoking.  In  1907  Hesse 
found  similar  pressure  effects.  Nonsmokers  have  not  as  yet  been 
tested  in  numbers  to  afford  a  report.  Only  one  enters  this  series. 
He  showed  a  fall  of  0.3  in  visual  acuity.  Accommodation  fell  off 
15  millimeters.  There  was  apparent  reduction  in  retinal  contrastiv- 
ity  of  1  millimeter.  Some  giddiness  occurred  at  18  minutes  from 
start,  accompanied  by  slight  nausea. 

Aviation  medical  authorities  in  the  war  zone  have  remarked  that 
aviators  were  using  tobacco  excessively,  smoking  while  in  the  air  as 
well  as  incessantly  while  on  the  ground.  It  has  further  been  re- 
ported that  soldiers  on  the  western  front  have  frequently  complained 
of  night  blindness.  Some  of  these  cases  may  be  due  to  excessive 
tobacco  without  the  occurrence  of  a  typical  tobacco  amblyopia. 
Practically  the  same  results  as  have  been  obtained  by  smoking  one 
cigar  have  been  produced  by  the  inhalation  of  one  or  two  cigarettes. 

VI.— PSYCHOLOGY  DEPARTMENT. 

I.   THE  RELATION  OF  PSYCHOLOGY  TO  THE  AVIATOR. 

The  function  of  psychology  in  respect  to  the  aviator  is  to  study 
his  adaptability  to  the  work  required  of  him.  Assuming  that  the 
determinable  structural  qualifications  of  the  aviator  are  adequate, 
that  his  more  mechanical  physiological  functions  are  satisfactory,  it 
is  yet  necessary  to  determine  the  conscious  or  integrative  action  of  his 
organism,  with  regard  to  the  adaptations  which  contribute  to  the 
composition  of  a  good  flier;  and  further,  his  adaptability  to  one  or 
another  set  of  requirements  for  different  departments  of  the  flying 
work. 

Obviously,  these  determinations  may  be  made  by  the  trial  and 
error  method  (which  in  this  case  is  merely  a  survival  method),  and 
this  has  been  followed  to  a  large  extent  in  several  foreign  air  services^ 
The  candidates  are  roughly  selected,  and  those  who  do  not  success- 
fully adapt  themselves  to  the  general  or  specific  requirements  prac- 
tically eliminate  themselves.  This  method  is,  however,  believed  to 
be  wasteful,  and  undoubtedly  a  more  economical  method  can  be  suc- 
cessfully followed. 

The  contribution  which  psychology  can  make  to  the  efficiency  of 
the  Air  Service,  in  view  of  the  foregoing,  can  be  summarized  under 
eight  heads: 

1.  The  adaptability  of  the  individual  to  the  general  requirements 
of  the-  service  may  be  determined.  Some  of  these  requirements  may 
be  enumerated  in  a  list  not  intended  to  be  exhaustive. 


164  MANUAL  OF  MEDICAL  BESEARCH   LABOBATORY. 

I.  Perception  (including  discrimination).    The  ability  to  perceive 
accurately  and  quickly  through  the  various  senses  (visual,  auditory, 
tactile,  muscular  and  articular,  and  visceral),  which  are  important 
for  the  flier,  depends  not  merely  on  the  perfection  of  the  sense  organs, 
but  also  on  the  integrative  action  by  which  definite  and  useful  per- 
ceptual reactions  are  achieved. 

II.  Control  of  "voluntary"  activity,  i.  e.,  of  that  activity  which 
must  vary  in  its  expression  according  to  the  variations  in  the  environ- 
ment.   Such  activity  is  truly  integrative  and  is  in  general  a  part  of 
the  perceptual  process. 

III.  Maintenance  of  equilibrium,  and  orientation.    The  complex 
mechanism  by  which  the  flier  preserves  his  balance,  and  the  more 
complex  mechanism  by  which  he  finds  his  way  about,  are  so  inter- 
connected tKat  they  necessarily  must  be  treated  together,  although 
the  functions  are  widely  different.    To  a  large  extent  these  functions 
are  automatic   (mechanical),  yet  both  involve  all  the  senses  enu- 
merated above  and  involve  in  both  cases  more  or  less  integration  of 
the  nervous  system. 

IV.  Memory  (in  the  sense  of  retentiveness)  is  dependent  on  con- 
ditions which  are  apparently  in  part  constitutional,  and  in  part  sub- 
ject to  control,  although  the  detailed  basis  of  these  conditions  is  not 
at  present  known. 

V.  Associative  thinking,  which  depends  on  retentiveness  and  ex- 
presses itself  in  the  various  forms  of  judgment,  inference,  and  de- 
cisions, is  an  integrative  function  closely  connected  with  perception, 
but  by  no  means  varying  directly  with  it  in  efficiency.    It  is  becoming 
more  and  more  clear  that  thinking,  like  perception,  is  a  conscious 
reaction  of  the  organism,  and  can  be  adequately  treated  only  as  such. 

VI.  Emotional  response :  Emotions  are  directly  connected  with  the 
driving  force  of  the  organism,  and  are  in  the  highest  degree  im- 
portant in  all  mental  processes.     The  Darwinian  point  of  view  of 
emotion   (as  developed  by  James,  Sutherland,    and    especially   by 
Lange),  that  it  is  a  bodily  (chiefly  viceral)  condition  or  process,  is 
more  and  more  becoming  indispensible  for  practical  consideration  of 
the  emotional  life. 

VII.  Attention,  which  is  the  direct  expression  of  the  degree  and 
completeness  of  integration,  is  of  especial  importance.    Not  only  the 
extent  to  which  the  flier  can  subordinate  all  other  reactions  to  the 
vital  reaction  of  the  moment,  and  the  length  of  time  during  which 
the  vitally  important  details  of  the  situation  which  confronts  him 
can  continue  to  dominate  his  nervous  system  in  spite  of  distractions 
(the  power  of  sustaining  attention,  as  we  commonly  express  it)  ; 
but  also  the  proper  balance  in  integration  (the  power  of  attending 
efficiently  to  several  distinct  details  in  a  situation),  need  to  be  studied 
very  carefully. 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  165 

VTII.  Habit  formation,  or  learning,  which  is  the  modification  of 
the  integrative  system  (it  may  be  the  modification  of  perception  and 
motor  control,  or  of  thinking  process),  is  a  topic  of  especial  im- 
portance in  flying  and  is  one  concerning  which  psychologists  have 
acquired  a  large  amount  of  information  in  recent  years. 

A  knowledge  of  the  precise  requirements  for  the  flier  in  all  these 
directions  is  yet  to  be  obtained.  Various  opinions  have  been  ex- 
pressed as  to  the  requirements,  but  psychologists  are  unanimously  of 
the  opinion  that  any  conclusions  in  these  matters  should  be  reached 
by  systematic  observations  and  experiments.  In  this  laboratory 
work  on  these  problems  is  being  carried  on  by  men  who  have  so  far 
attained  results  which  are  distinctly  encouraging,  but  not  yet  in  a 
stage  where  the  communication  thereof  is  feasible. 

2.  The  adaptability  of  the  aviator  to  special  requirements  of  the 
different  departments  of  flying  work :  The  same  work  is  not  required 
of  observers  as  is  required  of  pilots,  and  bombing  and  combat  do  not 
require  exactly  the  same  sort  of  pilot  work.    The  list  of  special  quali- 
fications will  probably  grow,  as  aviation  develops,  but  so  far  little 
has  been  done  in  the  way  of  determining  and  measuring  the  special 
qualifications.     Work  has  been  undertaken  in  this  line  and  results 
will  be  forthcoming  in  due  time. 

3.  Special  conditions  to  which  the  flier  may  be  subjected :  Probably 
the  most  important  special  condition  is  the  combination  of  cold  and 
low  oxygen  tension  encountered  at  high  altitudes.    While  nothing  has 
yet  been  done  in  the  Medical  Research  Laboratory  on  the  temperature 
problem,  a  great  deal  has  been  done  on  effects  of  insufficient  oxygen 
supply.     In  addition  to  the  physiological  effects  of  asphyxiation, 
there  are  distinct  psychological  effects   which   have   been   carefully 
studied  by  the  psychology  section.     Although  we  have  recognized 
from  the  beginning  that  tests  for  asphyxiation  effects,  and  the  grad- 
ing of  fliers  on  the  basis  of  their  endurance  of  oxygen  deprivation, 
are  of  minor  importance  as  compared  with  tests  in  the  other  direc- 
tions indicated  above  (since  the  evil  effects  of  the  low  oxygen  tension 
of  the  upper  atmosphere  can  in  most  cases  be  obviated  by  administer- 
ing oxygen  to  the  flier),  nevertheless  it  was  necessary  to  get  this 
problem  out  of  the  way  before  other  problems  could  be  attacked. 
Full  details  of  the  psychological  tests  and  ratings  for  'oxygen  short- 
age are  given  in  a  later  chapter. 

4.  Deterioration:  Assuming  that  the  individual  flier  is  fit  for  his 
job  and  properly  trained,  we  nevertheless  find  that  he  may  suffer 
deterioration,  both  of  a  temporary  sort  and  of  the  more  lasting  sort, 
which  is  frequently  designated  as  "staleness."    The  fact  that  an 
individual  when  in  his  best  trim  is  a  high-class  flier  and  efficient  in 
his  especial  department  of  flying  does  not  promise  that  he  will  re- 


166  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

main  such;  the  fact  that  an  individual  shows  high  capacity  for 
endurance  of  oxygen  shortage  does  not  signify  that  he  is  in  good 
flying  condition,  although  it  is  known  that  deterioration  in  certain 
conditions  requisite  for  flying  will  reduce  the  individual's  ability  to 
withstand  oxygen  shortage. 

Although  it  is  believed  that  in  certain  cases  psychological  causes 
(worry,  fear)  may  be  responsible  for  deterioration,  there  is  probably 
a  more  important  range  of  physiological  causes  operative.  In  all 
these  cases,  however,  mental  symptoms  are  produced,  since  it  is  pre- 
cisely in  the  failure  to  integrate  properly  rather  than  in  specific 
failure  of  sense  organ  or  muscles,  that  "  staleness  "  shows  itself.  The 
discovery  of  the  symptoms  and  the  development  of  tests  which  shall 
reveal  them  as  early  as  possible  is  undoubtedly  one  of  the  most  im- 
portant contributions  psychology  can  make  to  aviation,  since  it  is 
important  that  the  symptoms  be  detected  in  the  earliest  possible 
stage.  The  task  is  being  undertaken,  and  we  have  reason  to  be  con- 
fident it  will  be  successfully  carried  out  i  f  the  work  continues. 

From  the  foregoing  presentation  it  she  ild  be  evident  that  a  num- 
ber of  diverse  problems  confront  us.  The  requisite  tests  of  general 
ability  and  of  special  abilities  must  be  worked  out  conjunctively,  but 
are  not  capable  of  combination.  Certain  of  these  tests  which  are 
capable  of  repetition  may  be  useful  in  determining  an  aviator's  con- 
dition (for  detecting  deterioration),  but  the  applicability  of  these 
or  any  other  tests  for  deterioration  must  be  worked  out  independ- 
ently. It  is  especially  important  to  note  that  psychological  tests 
for  endurance  of  special  conditions  (oxygen  shortage),  if  adequate 
for  their  purpose,  can  not  give  any  reliable  evidence  on  general  or 
other  special  qualifications  or  on  deterioration. 

II.     PSYCHOLOGICAL,    RATING    OF    AVIATORS    FOR    ALTITUDE    LIMITS. 
OUTLINE   OF   CONDITIONS. 

The  work  on  oxygen  deficiency  has  so  far  been  principally  under 
the  conditions  established  by  the  rebreathing  apparatus,  with  some 
check  experiments  in  the  low-pressure  chamber.  With  this  appara- 
tus it  is  possible  to  produce  the  oxygen  tension  in  respired  air  equiva- 
lent to  the  tension  for  any  elevation  up  to  that  at  which  the  patient 
can  no  longer  endure  the  deficiency. 

The  chief  respiratory  differences  between  the  rebreathing  con- 
ditions and  those  actually  obtaining  in  the  upper  atmosphere  are 
(1)  the  greater  density,  (2)  the  greater  moisture  (practically  satu- 
ration), (3)  the  higher  temperature  of  the  air  in  the  rebreathing 
machine,  and  (4)  the  method  of  breathing,  through  the  mouth,  with 
the  machine.  While  it  is  possible  that  one  or  another  of  these  dif- 
ferences (most  probably  the  third)  may  make  a  difference  in  the 


MANtTAL  OF   MEDICAL  RESEARCH   LABORATORY.  167 

case  of  prolonged  holding  of  the  patient  at  certain  altitudes,  for 
rapid  "  ascents"  (i.  e.,  passages  from  normal  to  low  oxygen  tension), 
the  first  two  differences  do  not  seem  important.  There  has  been  as 
yet  no  means  of  testing  the  contributory  effect  of  temperature,  and 
it  has  not  been  possible  to  make  a  sufficiently  thorough  comparison 
of  the  effects  of  rebreathing  with  those  of  the  low-pressure  chamber. 
The  discomfort  of  the  mouth  breathing  is  undoubtedly  important  in 
individual  cases,  and  hence  interferes  somewhat  with  the  adequate 
rating  of  the  aviators,  but  in  the  cases  of  experienced  subjects  is  a 
minor  matter  and  has  no  important  bearing  on  the  scientific  conclu- 
sions. 

PSYCHOLOGICAL   EFFECTS. 

The  psychological  effects  of  oxygen  deficiency. — The  effects  of  oxy- 
gen insufficiency  upon  the  psychological  process  have  been  from  the 
beginning  of  our  work  studied  empirically,  with  the  least  possible 
hypothetical  guidance.  A  wide  range  of  details  of  mental  life  have 
been  investigated,  the  order  and  method  of  investigation  being  prac- 
tically directed  by  the  working  tests  which  were  available  or  which 
we  have  been  able  to  devise.  Hence  our  results  are  capable  of  throw- 
ing a  light  on  the  fundamental  principles  of  psychology. 

These  results  square  distinctly  with  the  conception  of  psychological 
processes  as  integrative,  i.  e.,  as  dependent  on  the  integration  of  the 
central  nervous  system,  the  working  together  of  the  system  as  a 
whole,  rather  than  on  the  action  of  any  specific  parts  of  the  system. 

The  basic  and  important  psychological  effects  of  asphyxiation  are 
on  voluntary  coordination  and  attention.  Until  asphyxiation  reaches 
the  stage  in  which  the  integrative  mechanism  is  -rapidly  approaching 
the  condition  of  complete  unconsciousness;  no  effects  are  demonstrable 
which  are  not  clearly  the  failure  of  the  one  or  the  other,  or  both,  of 
these  two  mental  factors.  In  the  prefinal  stages  perception  is  as  effi- 
cient as  the  muscular  control  of  the  sense  organs  and  organs  of  expres- 
sion and  the  power  to  attend  to  the  stimuli  permit.  Discriminative 
judgment,  likewise,  shows  no  falling  off  in  rapidity  or  accuracy  ex- 
cept as  impaired  motor  control  and  attention  produce  it.  Memory, 
with  "  immediate  memory,"  as  tested  by  the  ability  to  produce  what 
has  been  perceived  or  learned  immediately  before,  and  "true  mem- 
ory," as  tested  by  the  ability  to  produce  something  which  has  been 
"  latent "  for  a  certain  interval  after  being  learned  are  apparently  not 
affected  except  as  the  inability  to  attend  to  the  details  in  learning  or 
in  reproducing  or  inability  to  control  the  muscular  mechanism  of 
expression  may  enter. 

The  efficiency  of  limited  neuro-muscular  groups,  as  indicated  by 
dynamometer  tests,  is  not  impaired  in  the  prefinal  stages  of  asphyxia- 
tion. 


168  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

As  instances  of  tests  involving  perception  and  discrimination,  we 
may  cite  the  copying  of  a  list  of  work  and  the  translation  of  words 
into  code.  In  both  of  these  cases  speed  and  accuracy  are  maintained 
up  to  the  final  stages  of  asphyxiation,  provided  the  muscular  mech- 
anism of  accommodation  and  convergence  are  not  seriously  affected, 
although  the  mechanism  for  handwriting  may  be  so  affected  that  the 
written  results  of  the  list  are  legible  with  difficulty. 

In  more  complicated  discrimination,  where  rapid  and  accurate 
recognition  and  classification  of  material  are  required,  the  results  are 
similar.  Ability  to  remember  and  to  chart  correctly  the  relative 
spacial  position  of  objects  remains  normal  within  the  limits  of  ability 
to  make  adequate  movements  of  the  hand  in  charting. 

It  is  interesting  to  note  that  the  sensitivity  and  acuity  of  the  sense 
organs  shows  no  consistent  impairment  and  that  apparently  the  speed 
of  simple  reactions  (the  simple  reactions  do  not  in  general  require  a 
high  degree  of  integration)  is  not  intrinsically  reduced.  More  work 
remains  to  be  done  on  simple  reactions,  however,  before  definite  state- 
ments can  be  made.  The  distinctive  effec •(  on  the  nervous  system,  in 
short,  seems  to  be  a  change  in  its  integrative  action  and  not  a  change 
in  the  irritability  or  efficiency  of  any  particular  part  or  unit.  In  this 
respect  the  whole  picture  of  asphyxiation  from  a  psychological  point 
of  view  is  strongly  suggestive  of  the  picture  of  progressive  alcoholic 
intoxication. 

There  is  some  evidence  that  practice  in  enduring  asphyxiation  has 
value  in  increasing  the  efficiency  of  the  individual  under  a  certain 
degree  of  asphyxiation.  Expressed  in  untechnical  terms,  the  indi- 
vidual may  learn  to  husband  his  resources  and  by  applying  his  ca- 
pacity to  the  tasks  in  hand  accomplish  more  at  a  certain  level  than 
he  could  without  practice.  More  definite  statement  on  this  point 
can  not  be  made  on  the  basis  of  the  present  material.  It  is  not  pos- 
sible that  habituation  to  the  effects  of  alcohol  (not  to  regular  dos- 
ages) may  be  a  help  in  acquiring  ability  to  maintain  motor  and 
attention  efficiency  in  certain  degrees  of  asphyxiation. 

Training  of  another  sort  may  also  be  advantageous.  "  Grit "  counts 
in  the  maintenance  of  efficiency,  or  rather  the  maintenance  of  effi- 
ciency in  the  face  of  serious  oxygen  deficiency  is  "  grit,"  and  if  "  grit " 
in  one  task  or  situation  can  be  acquired  or  increased  by  training  in 
other  situations  (which  is  by  no  means  certain),  then  such  training 
is  advantageous. 

PRACTICAL  REQUIREMENTS. 

Under  the  practical  requirements  of  rating,  tests  must  be  single 
and  brief  during  progressive  depletion  of  the  oxygen  supply.  If 
many  individuals  are  to  be  examined  it  is  not  practicable  to  spend 
even  several  hours  on  each  one.  Hence  it  is  not  possible  to  hold  the 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  169 

subject  at  a  moderately  high  altitude  so  that  asphyxiation  effects 
will  eventually  appear.  Nor  is  it  possible  to  repeat  a  briefer  test  a 
number  of  times.  Hence,  the  subject  must  be  allowed  to  rebreathe 
rapidly  (during  not  much  over  a  half  hour  at  most)r  to  a  low  point 
of  oxygen  tension,  reaching  his  maximal  altitude  for  that  rate  of 
"  ascent."  It  follows  that  the  method  used  must  be  one  which  is  not 
approved  for  psychological  work  under  other  conditions  and  which, 
for  want  of  a  better  term,  is  called  clinical.  Thus,  since  the  sub- 
ject's condition  is  rapidly  changing  from  minute  to  minute,  the  ex- 
aminers must  be  able  to  determine  the  psychological  condition  at  any 
minute  and  can  not  use  the  method  (more  exact  under  other  condi- 
tions) of  determining  the  average  speed  and  accuracy  of  work  done 
during  a  period  of  several  minutes. 

A  final  composite  reason  for  using  a  clinical  method  comes  from 
the  need  for  rapid  work.  Graphic  methods  might  be  employed,  but 
would  largely  hinder  the  expedition  of  the  work  on  account  of  the 
time  and  labor  needed  for  their  interpretation.  Moreover,  in  such 
rapid  work  fineness  of  gradation  in  rating  would  be  seriously  mis- 
leading, hence  the  greater  exactness  of  the  graphic  method  would  be 
largely  illusory.  For  research  purposes,  on  the  other  hand,  the  mat- 
ter is  entirely  different. 

Fatigue,  also,  must  enter  into  the  test  as  little  as  possible,  else  the 
deterioration  in  performance  due  to  fatigue  will  confuse  the  de- 
termination of  the  asphyxiation  effects. 

Since  the  test  can  not  be  repeated,  it  is  important  that  there  shall 
be  little  practice,  effect  in  the  work  required,  else  the  individual 
variation  in  rates  of  learning  will  prevent  the  fair  determination  of 
the  relative  susceptibility  of  the  different  subjects  to  the  oxygen 
deprivation,  which  is  the  sole  point  to  be  considered. 

It  was  early  discovered  that  under  asphyxiation,  as  under  alcoholic 
intoxication,  it  is  possible  for  a  reactor  to  "  pull  himself  together  " 
for  a  brief  space  of  time  (a  minute,  or  even  several  minutes),  during 
which  his  efficiency  on  a  set  task  may  be  as  high  as  (or  even  higher 
than)  his  normal,  at  the  termination  of  the  task  sinking  to  a  relatively 
low  level  of  efficiency.  If  given  a  series  of  tasks,  with  brief  resting 
intervals  between,  the  reactor  may  therefore  accomplish  a  perform- 
ance which  is  practically  normal,  even  up  to  a  minute  or  two  before, 
the  point  at  which  complete  lapse  of  integration  occurs.  In  this  way 
his  real  psychological  deterioration  may  be  masked.  It  is  necessary, 
therefore,  to  set  a  task  which,  although  minimally  fatiguing,  is  prac- 
tically continuous,  allowing  the  reactor  no  expected  periods  in  which 
no  work  will  be  demanded  of  him,  and  thus  preventing  him  from 
making  use  of  attention  peaks  as  the  phases  of  "pulling  himself 
together  "  may  justly  be  called. 


170  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

In  determining  the  sensitivity  or  acuity  of  sense  organs,  on  the 
other  hand,  the  "  attention  peaks  "  are  precisely  in  order,  and  pause 
should  be  taken  to  present  the  stimuli  at  the  highest  peaks. 

Many  tests  which  otherwise  would  be  applicable  impel  the  subject 
(reactor)  to  hold  his  breath  during  the  crucial  moments  of  the  test. 
The  conventional  steadiness  test  is  of  this  character.  If  the  reactor, 
already  suffering  from  oxygen  deficiency,  holds  his  breath  for  20 
seconds,  or  largely  reduces  his  breathing  during  that  perio'd,  he 
makes  an  important  change  in  his  oxygen  supply,  a  change,  more- 
over, which  can  not  be  measured.  Hence  the  purpose  of  the  test  is 
largely  defeated.  The  steadiness  test,  and  others  in  this  class,  which 
may  show  marked  effects  of  low-oxygen  tension,  can  not  be  used. 

Although  it  is  desirable  that  the  test  employed  shall  in  some  degree 

correspond  to  the  aviator's  actual  task  in  flying,  it  is  important  that 

it  shall  not  use  any  of  the  movements  or  discrimination  involved  in 

"flying,  else  it  would  be  impossible  to  rate  fairly  both  those  with  and 

without  experience  in  planes. 

A  final  composite  reason  for  using  a  "  clinical "  method  comes  from 
the  need  for  rapid  work.  Graphic  records  might  be  employed,  but 
would  largely  hinder  the  expedition  of  the  work  on  account  of  the 
time  and  labor  needed  for.  their  interpretation.  Moreover,  in  such 
rapid  work  fineness  of  gradation  in  rating  would  be  seriously  mis- 
leading, hence  the  greater  exactness  of  graphic  methods  would  be 
largely  specious.  For  experimental  work  the  matter  is  entirely 
different. 

In  addition  to  general  limitations  of  method  and  apparatus  due 
to  necessary  working  conditions,  there  are  specific  limitations  im- 
posed by  the  rebreathing  apparatus  and  the  cardiovascular  work 
which  must  be  simultaneous  with  the  psychological. 

I.  The  reactor  can  not  speak  on  account  of  the  mouthpiece.    This 
excludes  such  tests  as  the  association  reaction,  which  otherwise  might 
be  highly  useful. 

II.  The  reactor's  head  movements  are  narrowly  limited  and  his 
field  of  view  correspondingly  restricted.    This  is  not  a  very  serious 
limitation. 

III.  The  blood  pressure,  which  is  taken  throughout  the  test,  is 
taken  from  the  reactor's  left  arm.    This  further  limits  the  reactor's 
means  of  expression  to  one  arm  and  his  feet. 

APPARATUS  FOR  THE  STANDARD  TEST. 

The  apparatus  used  for  the  psychological  tests  consists  of  two 
groups,  (a)  and  (2>).  The  (a)  group  includes  a  number  of  pieces 
assembled  on  a  specially  designed  table,  adjustable  in  height  and 
slope,  and  swinging  on  a  single  heavy  post  mounted  on  a  cast-iron 
base.  This  table  is  designed  to  furnish  a  sufficiently  rigid  mounting 


170 


171 


MANUAL  OF   MEDICAL  EESEABCH   LABOEATOEY.  171 

and  at  the  same  time  give  greater  convenience  than  could  be  afforded 
by  a  table  with  legs. 

(a)  The  apparatus  mounted  on  the  table  form  three  separate  units, 
(1)  a  series  of  14  stimulus  lamps  (2  c.  p.)  arranged  in  two  rows  of 
seven  each,  with  two  similarly  arranged  rows  of  contact  buttons; 
each  surrounded  by  a  washer;  a  green  check  lamp  and  a  red  error 
lamp ;  and  a  stylus  with  a  hard  rubber  handle  and  metal  tip.    These 
parts  of  the  unit  are  so  wired  electrically  that  when  a  stimulus  lamp 
lights  the  corresponding  contact  button  is  "  alive,"  and  if  touched 
with  the  metal  tip  of  the  stylus  causes  the  check  lamp  to  light.    If 
the  washer  surrounding  any  of  the  buttons  is  touched  with  the  stylus 
at  any  time,  the  error  lamp  lights. 

(2)  Two  ammeters  mounted  on  a  metal  arm'  above  the  table  top 
are  connected  in  series  with  two  rheostats,  one  on  the  upper  side 
of  the  table  top  at  the  edge  nearer  the  reactor,  the  other  underneath, 
at  the  edge  nearer  the  psychologist.    One  ammeter  faces  the  reactor, 
the  other  the  psychologist.    A  change  in  the  resistance  made  by  the 
psychologist  at  his  rheostat,  causing  a  change  in  the  ammeter  reading, 
may  be  compensated  for  by  a  change  in  the  reactor's  rheostat,  by 
which  the  original  ammeter  reading  may  be  restored. 

(3)  A  small  electric  motor  mounted  on  the  upper  side  of  the  table 
top  is  connected  in  series  with  a  third  rheostat  underneath  the  table. 
A  two-way  lever  switch  mounted  underneath  the  table  at  the  edge 
next  to  the  psychologist  and  a  rocking  pedal  two-way  switch  on  the 
floor  under  the  table  are  connected  with  the  rheostat  by  a  three- wire 
system,  so  that  a  part  of  the  resistance  of  the  rheostat  can  be  cut 
out  (thus  increasing  the  speed  of  the  motor)  by  either  switch  and 
again  cut  in  (thus  restoring  the  lower  motor  speed)  by  either  switch. 

(b)  The  second  group  of  apparatus,  on  a  small  table  in  any  con- 
venient part  of  the  room,  consists  of  either  a  button  board  having  14 
buttons,  corresponding  to  the  14  stimulus  lamps,  or  of  an  automatic 
distributor  which  lights  the  stimulus  lamps  in  selective  order  and 
times  their  duration.     With  the  button  board  an  automatic  flash 
timer  may  be  used,  requiring  an  assistant  merely  to  select  the  buttons, 
or  the  assistant  may  time  the  flasher  with  a  stop-watch  as  well  as 
select  the  buttons. 

The  («)  and  (b)  groups  of  apparatus  are  provided  with  trans- 
formers to  adapt  the  electric  current  to  the  2  c.  p.  lamps,  and  are 
electrically  connected  with  either  and  with  the  source  of  120  volt 
a.  c.  current  by  flexible  cables. 

Method  of  conducting  the  test.  The  rebreathing  machine  should 
be  adjusted  by  the  physiologist  to  give  a  "  standard  run,"  which  will 
vary  in  time  according  to  the  individual  and  his  method  of  work, 
but  which  -will  bring  a  reactor  of  the  A  class  to  7  per  cent  of  oxygen 


172  MANUAL  OF   MEDICAL  EESEABCH   LABOBATORY. 

in  25  minutes  on  the  average.     For  this  standard  run  the  quantity 
of  air  in  the  tank  at  start  is  60  liters. 

The  reactor,  being  seated  in  proper  position  before  the  (a)  appa- 
ratus, is  given  the  following  instructions  in  printed  form : 

INSTRUCTIONS. 

BEAD    CABEFTTLLY. 

You  have  three  things  to  do : 

1.  Lights. 

When  a  light  flashes,  touch  with  the  stylus  the  top  of  the  corresponding  button. 
Do  not  touch  the  washer. 

2.  Ammeter. 

Watch  the  ammeter  and  by  adjusting  the  slide  of  the  rheostat  (using  the 
right  hand)  keep  the  ammeter  at  the  designated  mark. 

3.  Motor. 

Keep  the  motor  at  low  speed  by  maintaining  the  proper  positions  of  the 
pedal.  When  the  motor  speeds  up,  push  the  pedal  from  whichever  position  in 
which  it  may  be  (heel  down,  or  toe  down),  into  the  opposite  position,  and  leave 
it  in  the  new  position  until  the  speed  again  increases. 

NOTES. — (a)  The  lights  are  of  first  importance,  i.  e.,  if  a  light  appears  when 
you  are  reacting  (or  about  to  react)  to  the  ammeter-hand,  react  to  the  light 
first  and  then  go  back  to  the  rheostat. 

( 6 )  When  you  touch  with  the  stylus  a  contact-button  corresponding  to  a  light, 
the  movement  of  hand  and  arm  should  be  a  "  free  "  one  (neither  arm  nor  hand 
should  touch  table,  rheostat,  or  board ) .  The  hand  may,  at  other  times,  rest  on 
the  slide  of  the  rheostat. 

(c)  Do  your  work  with  ACCUBACY,  NEATNESS,  and  PROMPTNESS.  Do  not  bang, 
slam,  or  jab. 

While  the  reactor  is  reading  the  instructions,  the  psychologist  is 
ready  to  explain  any  detail  of  the  apparatus  or  method  in  which  the 
reactor  may  show  interest;  and  after  the  reactor  has  finished,  the 
psychologist  further  explains  the  procedure  and  verbally  emphasizes 
the  important  points  in  the  instruction. 

When  the  rebreathing  machine  is  ready  and  the  blood-pressure  re- 
corder has  secured  the  requisite  preliminary  readings,  the  mouth- 
piece and  nose  clip  being  in  place,  the  external  opening  of  the  mouth- 
piece is  closed  by  the  responsible  clinician  and  the  test  commences. 
The  psychologist  and  all  others  concerned  in  making  the  test  start 
their  stop  watches  at  the  moment  when  the  rebreathing  commences. 
The  psychologist  should  record  if  possible  the  time  which  elapses 
between  the  insertion  of  the  mouthpiece  and  the  commencing  of 
the  breathing,  unless  a  regular  routine  for  this  time  be  adopted. 

During  the  first  three  minutes  of  the  test  the  psychologist  coaches 
the  reactor  if  necessary  and  estimates  his  comprehension  of  the  task 


172 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  173 

\ 

and  instructions,  his  power  of  attention,  and  his  composure  (free- 
dom from  excitement  or  nervousness),  entering  these  on  the  record 
sheet  then  or  later  as  good,  fair,  or  poor.  He  should  also  note  the 
motor  tendencies  of  the  reactor,  and  if  these  fall  in  one  or  more  of 
the  following  categories  this  also  should  be  entered. 

JfOTOB   TENDENCIES. 

To  be  put  on  original  record  sheet  at  bottom;  on  official  sheet  under  general 
impressions,  psychological;  on  psychology  record  card  under  notes: 

(1)  Tremor. 

(2)  Tense. 

(3)  Impulsive. 

(4)  Steady. 

(5)  Rapid. 

(6)  Slow. 

(7)  Hesitant. 

(8)  Accurate. 

(9)  Inaccurate. 

(10)    (Combinations  of  above.) 

Enter  merely  the  appropriate  type  word  or  words ;  it  is  not  necessary  to 
write  "  motor  tendencies." 

In  addition  to  these  general  tendencies,  it  is  important  that  the 
psychologist  take  notice  of  the  specific  tendencies  shown  by  the  re- 
actor, and  if  definite  types  of  error  are  shown,  watch  during  the 
succeeding  five  or  six  minutes  for  improvements  in  these  details.  In 
this  way  the  "M"  and  "A"  determination  described  below  may  be 
accurately  noted  as  deterioration  from  the  normal  proficiency  of  the 
reactor,  and  not  as  failures  with  regard  to  an  absolute  standard. 
This  is  important,  since  the  rating  on  these  tests  is  valid  only  as  an 
index  of  the  effects  of  asphyxiation  and  not  as  an  index  of  effi- 
ciency or  inefficiency  in  any  other  respect.  The  comprehension,  at- 
tention, composure,  and  motor  entries  are,  however,  worth  record- 
ing in  order  that  this  data  may  be  used  later  for  purposes  other 
than  oxygen  rating. 

Normally  the  test  continues  until  complete  inefficiency  is  reached, 
at  which  point  the  psychologist  must  sharply  notify  the  responsible 
medical  attendant  in  order  that  the  reactor  may  at  once  be  given  air, 
and  so  prevented  from  undergoing  the  collapse  which  would  ensue  in 
a  minute  or  so. 

The  recognition  of  complete  inefficiency  is  a  matter  on  which  the 
psychologist  must  carefully  train  himself.  In  general  it  shows  in  a 
definite  way,  as  described  below,  but  may  show  in  forms  which 
are  readily  recognized  by  the  trained  observer  but  described  with 
difficulty. 

In  many  cases  the  responsible  medical  attendant  will  find  it  neces- 
sary to  stop  the  test  because  of  dangerous  cardiovascular  symptoms 
before  inefficiency  is  reached. 


174  MANUAL   OP    MEDICAL  BESEAECH   LABOEATOEY. 

t 

In  commencing  work  on  the  reactor  it  is  advisable  to  allow  him 
to  react  to  the  lights  alone  during  the  first  minute  and  add  suc- 
cessively the  changes  in  the  motor  noise  and  in  the  ammeter  read- 
ings. He  should  be  working  on  all  three  tasks  by  the  middle  of  the 
third  minute. 

In  observing,  the  psychologist  needs  to  attend  as  constantly  as 
possible  to  the  behavior  of  the  reactor,  and  hence  must  reduce  the 
labor  of  recording  to  a  minimum.  For  this  purpose  and  for  the 
purpose  of  standardizing  the  method  of  observation  the  following 
symbols  have  been  adopted : 

SYMBOLS   AND  THEIR   SIGNIFICANCE. 

— >      Rebreathing  starts. 

W       Work  begins. 

^      First  significant  effects  on  "voluntary  coordination." 

^  "Fumbling " ;  clumsy;  inaccuracy  in  touching  targets. 
"Groping";  approaching  target  with  corrective  move- 
ments. Usually  a  compensation  for  Q. 

E  Increased  "effort"  or  force  in  applying  stylus  to 
targets. 

3       Decreased  effort. 

I        "Impulsive"  or  uncontrolled  movements: 

a,  on  the  outward  movement;  to  the  target. 

b,  on  the  return  movement. 
S       Slowing  of  reactive  movements. 

F       Speeding  of  reactive  movements. 
^      First  significant  effects  on  "attention." 
d£      "Distraction"  from  lights,  neglects  lights. 
clt-tv    Neglects  lights  for  voltmeter. 
/        (Contraction  for  dll.)     Reactor    delays    initiating 
stylus  movement  so  long  that  he  fails  to  light 
check  lamp. 
//      Reactor  delays  so  long  that  he  touches  the  target 

after  light  has  gone  out. 

///      Reactor  starts  movement  after  light  has  gone  out.' 
I IJ I     Reactor  makes  no  attempt  to  initiate  light  reaction. 
cU>-      "Distraction"  from  the  dial;  neglects  to  note  and 

adjust  the  position  of  the  index  hand. 
d/w      "Distraction"  from  the  noise;  neglects  to  control  the 

speed  motor. 
/  Gt  /    Confusion  between  rows  of  lamps;  but  finally  touches 

the  right  target. 
(7£      Confusion  between  columns  of  lamps;  but  finally 

touches  the  right  target. 
Selecting  target  in  wrong  row. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  175 

u>t  Selecting  target  in  wrong  column. 

Wv  Wrong  direction  on  the  dial. 

WN  Wrong  shift  of  pedal. 

<^>  Two  of  the  symptoms,  <p,    /,  I,  and  E,  repeatedly. 

In  certain  cases,  exaggeration  of  one. 

<£>      Two  of  the  symptoms,  dl,  d/v,  d/w,  ///,  /Gt/,  Ct, 
Zv.     In  certain  cases,  exaggeration  of  one. 

O  "  Inefficiency."  Inability  to  control  any  of  the  three 
tasks.  The  reactor  sometimes  stares  at  the  lights 
without  making  any  attempt  to  touch  the  target; 
or  makes  merely  irrelevant  touches.  Completely 
disregarding  L  and  N.  Sometimes  he  develops 
severe  tremors  or  jerks  which  render  it  impossible 
to  work.  Occasionally  a  reactor  develops  unique 
symptom  at  this  point. 

*  Breakdown.  Reactor  ceases  to  work  and  commences 
to  collapse.  This  comes  very  soon  (30".  to  2') 
after  0;  is  qualitatively  a  much  more  serious  con- 
dition. 

X      Reactor  "  taken  off."     Air  or  oxygen  given  him. 

ADDITIONAL  SYMBOLS   FOR   SYMPTOMS   WHICH  MAY  BE   OF  DIAGNOSTIC 

AID. 


Tremor  of  the  hand. 
Jerkiness  of  the  hand. 
H       Swaying  or  drooping  of  the  head. 
T       Taps  button  more  than  once. 
R      Rests  hand  or  fingers  while  touching  button. 
K      Keeps  stylus  on  button  after  making  touch. 
In  general,  the  "arrowheads"  (—  >)  and  "diamonds"  (0)  are  not 
inserted  until  after  the  test  is  finished. 

On  the  completion  of  the  test  the  entries  on  the  record  sheet  are 
completed,  and  the  material  is  now  ready  for  rating,  which  is  done 
on  the  following  basis  : 

RATING  SCHEME. 

1.  Take  25  minutes  as  the  standard  duration  of  a  run.    If  the  O  or  X 
appears  before  the  end  of  25  minutes,  debit  one  point  for  each  minute  ; 
similarly,  credit  one  point  for  each  minute  in  case  O  or  X  appears 
after  25  minutes. 

2.  Assume  as  a  standard  of  altitude  7  per  cent  of  oxygen  for  O  or 
X.    Debit  or  credit  one  point  for  $ach  ^  of  1  per  cent. 

3.  As  in  the  case  of  1,  take  25  minutes  as  the  standard  time  for  the 
appearance  of  both  of  the  two  diamonds.    Debit  or  credit  one  point 
for  each  minute  as  above. 


176  MANUAL  OP  MEDICAL  RESEARCH  LABORATORY. 

4.  Assume  15  minutes  as  the  standard  time  for  the  appearance  of 
both  the  two  arrowheads.    Debit  or  credit  for  each  minute  as  above. 

5.  If  the  record  of  the  subject  tested  be  such  that  either  arrowhead 
or  either  diamond  can  not  be  entered,  compute  the  symbol  in  question 
as  if  it  fell  at  the  point  of  O  (or  X,  if  O  be  not  reached;  see  para- 
graph 6,  below). 

6.  Add  the  debits  and  credits,  and  assign  to  class  as  follows : 

+n 0  Class  A+ 

0 —12  Class  A— 

—12 —30  Class  B 

—30 — n  Class  C 

7.  Where  an  oxygen  tension  of  8  per  cent  or  less  is  not  attained  in 
less  than  30  minutes,  a  grade  above  B  shall  not  be  assigned.    For 
runs  reaching  a  low  percentage  (below  7  per  cent)  in  less  than  22 
minutes,  discretion  may  be  exercised  in  debiting  for  earliness  of 
symbols.    Such  short  runs  are  especially  to  be  avoided  if  possible. 

8.  For  a  definite  rating  O  must  be  used.    However,  in  case  the  test 
was  stopped  by  the  clinician  without  reaching  O,  the  tentative  rating 
may  be  computed  from  X.    If  this  tentative  rating  is  A,  it  is  to  be 
entered  as  such.    If,  however,  the  tentative  rating  is  of  a  lower  class, 
it  is  to  be  entered  with  the  addition  "  or  higher."    This  phrase  "  or 
higher"  shall  always  indicate  that  the  reactor  was  removed  before 
reaching  (O),  and  not  at  the  instance  of  the  psychologist.     It  is 
not  to  be  entered  in  any  other  case. 

On  first  glance-  the  rating  scheme  seems  to  be  based  on  time  rather 
than  on  oxygen  percentage,  but  this  is  only  apparent.  If  every  re- 
actor was  run  through  at  the  same  rate,  for  example,  a  rate  of  oxygen 
depletion  at  which  7  per  cent  would  be  reached  in  25  minutes,  it 
would  be  immaterial  whether  the  oxygen  percentages  or  the  times  at 
which  the  arrowheads,  diamonds,  and  circles  are  reached  should  be 
used,  since  there  would  be  a  fixed  correspondence  between  these. 
Since  rates  vary  in  accordance  with  the  individual  rates  of  oxygen 
consumption,  and  since  a  faster  rate  enables  the  reactor  to  reach  a 
lower  percentage,  and  a  slower  rate  brings  inefficiency  at  a  higher 
percentage-  it  is  necessary  to  make  allowance  for  the  variations  in 
rate.  This  can  be  done  either  by  computing  in  oxygen  percentages, 
and  then  making  a  correction  for  the  time,  or  more  simply,  as  in  the 
scheme  actually  employed,  by  computing  in  times,  as  if  the  oxygen 
change  followed  a  line  of  the  same  slope  in  each  case,  and  then  cor- 
recting for  deviation  from  this  slope  in  terms  of  the  final  oxygen 
percentages  reached. 

The  rating  scheme  is  adequate^to  classify  the  reactors  in  the  four 
groups  (A-plus,  A-minus,  B,  and  C),  provided  the  psychologist  who 
does  the  observing  also  does  the  rating,  and  exercises  due  judgment, 
based  on  his  general  observation  of  the  reactor's  work,  in  rating  those 


MANUAL  OF   MEDICAL  RESEARCH  LABORATORY.  177 

cases  which  lie  near  the  limits  of  the  several  classes.  The  scheme 
should  be  an  assistance  to  the  psychologist's  final  judgment,  not  a 
hampering  condition,  although  the  most  satisfactory  results  will  be 
obtained  by  relying  on  it  very  substantially. 

The  chief  difficulty  with  this  method  of  testing  is  in  the  heavy  and 
exhausting  labor  entailed  on  the  psychologist.  Necessarily  his  atten- 
tion is  kept  at  a  high  level  throughout  the  test,  and  it  has  already  be- 
come evident  that  a  full  daily  program  will  not  be  possible  as  a  con- 
tinuous thing.  It  is  hoped  that  it  will  be  possible  to  supply  two 
psychologists  with  each  testing  unit  of  which  heavy  duty  is  required, 
in  order  that  they  may  relieve  each  other  and  maintain  the  efficiency 
of  the  unit. 

In  making  the  test,  diligent  care  must  be  exercised  to  prevent  the 
reactor  from  being  anxious  or  alarmed  as  to  the  experience  he  is  to 
undergo.  Hence  no  remarks  must  be  made  in  his  presence  as  to  dan- 
ger or  serious  discomfort,  and,  if  necessary-  assurance  should  be 
given  that  the  test  makes  no  great  demands  on  the  reactor.  It  is 
also  important  that  instructions  be  given  in  a  routine  way,  the  same 
for  all  reactors ;  otherwise  the  purposes  of  the  test  as  a  relative  rating 
scheme  are  in  part  defeated. 

The  temporary  physical  condition  of  the  reactor  is  also  a  matter 
which  should  be  carefully  considered.  Loss  of  sleep,  worry,  dissipa- 
tion, or  other  causes  which  reduce  general  resistance  are  apt  to  re- 
duce the  capacity  for  endurance  of  oxygen  deficiency,  and  produce  an 
earlier  onset  of  psychological  inefficiency  than  would  occur  under 
better  conditions. 

On  the  other  hand,  the  reactor  may  be  in  bad  shape  physically  or 
mentally  (from  worry,  etc.)  and  yet  make  a  very  good  record.  One 
reactor,  for  example,  who  made  an  unusually  good  record,  with  fine 
motor  control  and  efficient  attention  down  to  a  low  percentage  of 
oxygen,  had  had  but  a  few  hours  sleep  in  48  hours,  felt  in  "  rotten  " 
shape,  and  expressed  himself  anxious  to  come  back  when  he  felt  bet-' 
ter,  "  to  see  what  he  really  could  do  on  the  test." 

In  short,  the  test  gives  a  measure  of  endurance  of  oxygen  deficiency 
solely,  and  while  this  endurance  may  be  affected  by  a  variety  of 
factors,  it  gives  no  measure  of  these  factors. 

Some  incidental  results  of  the  work  on  rebreathing. — It  is  apparent 
that  a  great  deal  which  has  come  to  light  in  the  course  of  the  work 
will  be  of  value  for  work  more  or  less  closely  allied.  Findings  in 
regard  to  the  precise  effect  of  oxygen  shortage,  and  the  concealment 
of  these  effects  through  "  attention  peaks  "  point  to  an  application, 
with  a  possibility  of  clearing  up  certain  puzzling  results  of  earlier 
work.  The  same  application  may  be  made  in  studies  of  fatigue, 
in  which  in  the  past  no  great  success  has  been  attained  with  psycho- 
89119—18 12 


178  MANUAL   OP   MEDICAL  RESEARCH   LABORATORY. 

logical  tests.     Alcohol  and  drug  effects  may  also  be  attacked  anew 
in  the  light  of  the  present  work. 

The  relation  of  certain  emotional  states  to  systolic  pressure  has 
also  appeared  in  an  interesting  way.  The  conspicuous  thing  which 
has  come  out  is  that  apprehension — the  feeling  which  can  be  de- 
scribed as  "now  we  are  off;  I  wonder  just  what  will  happen  to 
me" — is  associated  wiith  a  temporary  rise  in  systolic  pressure. 
Observation  in  these  effects  in  rebreathing  led  us  to  experiment 
with  various  expected  stimuli  (pretended  doses  of  drugs,  threatened 
stimuli  of  undescribed  kinds)  with  quite  uniform  results.  Where 
fear  enters,  the  systolic  rise  tends  to  be  sustained.  An  interest- 
ing series  of  observations  has  been  started  on  the  systolic  effect 
of  announcing  to  cadets,  waiting  on  the  field  for  instruction,  their 
turns  for  flight.  It  is  possible  that  very  practical  results  may  be 
obtained  in  this  way,  in  information  concerning  the  temperament  of 
the  cadets. 

III.  THE  PSYCHOLOGICAL  QUALIFICATIONS  OF  THE  FLIER. 

It  was  pointed  out  above  that  the  flier  needs  not  only  to  fly,  but 
also  needs  to  be  able  to  perform  definite  tasks — observing,  signaling, 
operating  a  machine  gun,  etc. — without  which  the  ability  to  pilot 
a  plane  would  be  of  little  military  use.  It  is  desirable,  therefore, 
to  determine,  in  so  far  as  it  may  be  possible,  the  aptitude  of  the 
candidate  for  the  acquisition  (in  the  ground  school)  of  the  funda- 
mental training  which  may  fit  him  for  the  required  range  of  work, 
and  to  determine  his  capacity  for  learning  and  performing  ade- 
quately the  tasks  for  which  the  ground  school  work  is  intended  to 
fit  him. 

To  a  certain  extent  a  survey  of  the  candidate's  school  and  college 
training  is  a  means  for  the  determination  of  his  possibilities,  since 
the  specific  sorts  of  training  he  has  already  received  are  thereby 
revealed,  and  since,  moreover,  such  schooling  is  in  itself  a  process 
of  elimination  of  those  who  are  not  intelligent  and  adaptable.  This 
method  of  determination  might  well  be  supplemented  by  "intelli- 
gence tests  "  of  the  customary  type ;  but  even  these  additions  would 
not  take  the  place  of  specific  tests  of  the  functions  which  are  known 
to  be  important  in  flying. 

The  important  problem  is  the  discovery  of  the  tests  which  shall  be 
practicable.  The  plan  which  we  have  followed  in  this  work  is,  first, 
to  develop  tests  which  promise  to  be  applicable  to  the  aptitudes  it  is 
desired  to  investigate ;  and  second,  to  give  the  tests  so  developed  to  a 
large  number  of  fliers  whose  actual  flying  ability  can  be  definitely 
known.  By  comparison  and  correlation  of  the  results  of  the  tests 
with  the  actual  efficiency  ratings  of  the  fliers,  it  is  possible  to  deter- 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  179 

mine  the  applicability  and  usefulness  of  the  tests.  In  some  cases  the 
development  of  the  test  itself  is  a  difficult  experimental  undertaking ; 
in  other  cases  the  tests  are  easily  obtained,  requiring  merely  the  ap- 
plication and  correlation. 

Evidence  of  flying  ability  is  obtained,  for  the  purpose  of  compari- 
son with  the  results  of  the  tests,  from  the  men  who  have  trained 
the  fliers  tested,  and  have  observed  their  individual  progress  in  the 
work  of  aviation.  The  value  of  any  test  of  a  specific  function  which 
may  be  important  for  aviation  must  ultimately  rest  solely  on  this 
comparison.  No  theoretical  considerations  of  the  qualifications  of  a 
flier  can  be  substituted  for  the  empirical  determination  of  the  relative 
flying  abilities  of  men  differing  in  respect  to  the  qualifications  in 
question. 

Experimental  work  on  the  problem  of  flying  qualifications  has  been 
done  at  San  Diego  and  Berkeley  and  is  in  progress  in  this  laboratory. 
Some  of  the  points  attacked  are : 

(1)  Reaction  to  auditory,  tactual,  and  visual  stimulations,  and  to 
changes  of  position  of  the  body:  The  time  required  for  reaction  to 
the  stimuli  of  the  sorts  mentioned  is  measured,  and  the  individuals 
are  rated  on  their  average  reaction  times  of  each  sort,  and  their 
variability.     While  nothing  important  is  to  be  expected  to  result 
directly  from  the  measurement  of  the  simple  reaction  times  to  sound 
light  and  touch,  even  the  negative  finding,  if  it  occurs,  is  important. 

(2)  Discrimination  time:  The  time  required  to  discriminate  accu- 
rately between  different  stimuli  suddenly  presented. 

(3)  Association  reaction  time:  The  time  required  to  reply  to  a 
spoken  word  with  another  word  which  is  related  to  the  stimulus  word 
in  a  prescribed  way.    For  example,  nouns  may  be  given  and  the  re- 
actor required  to  respond  in  each  case  with  an  adjective  appropriately 
modifying  the  noun ;  or  verbs  may  be  given  and  the  reactor  required 
to  respond  to  each  with  the  name  of  an  object  appropriate  for  the 
action  indicated  by  the  verb.    In  this  work  the  time  is  measured  and 
the  appropriateness  or  accuracy  of  the  response  is  evaluated  as  well. 

(4)  The  rate  at  which  a  person  can  learn  a  certain  complicated 
muscular  coordination  involving  the  hands  and  feet  in  somewhat  the 
way  required  in  piloting  a  plane. 

(5)  The  sensitivity  to  gradual  changes  in  the  position  of  the  body 
in  horizontal  and  vertical  planes.    Several  important  researches  are 
in  progress  on  points  connected  with  the  analysis  of  the  highly  com- 
plicated psycho-physical  mechanism  involved  in  the  maintenance  of 
equilibrium. 

(6)  The  capacity  to  acquire  certain  simple  forms  of  dexterity. 

(7)  The  temporal  and  other  conditions  of  the  appearance  of  the 
signs  of  fatigue. 


180 


MANUAL  OF   MEDICAL  RESEARCH    LABORATORY. 


There  are  also  in  progress  experiments  on  orientation ;  the  ability 
to  find  one's  way  about,  and  to  know,  from  moment  to  mo- 
ment and  from  position  to  position  the  direction  and  distances 
of  important  near  and  far  features  of  the  environment.  This 
may  readily  be  granted  to  be  a  topic  of  the  highest  importance  for 
aviation,  although  the  various  tests  which  are  being  developed  are 
not  yet  in  the  stage  of  application  to  aviators,  by  which  application 
only,  as  indicated  above,  can  the  practical  value  of  the  tests  be  de- 
termined. 

PSYCHOLOGICAL    INVESTIGATIONS    WITH    LOW    OXYGEN    TENSION. 

1.  Judgment. — A  test  of  judgment  has  been  carried  out  under 
supervision  by  enlisted  psychologists.  On  each  of  a  large  number  of 
blank  playing  cards,  a  nonsense  syllable  was  printed  in  large  letters : 
PEL,  GUJ,  KIM,  CEZ,  etc.  A  card  rack  with  five  compartments 
(fig.  4)  was  made,  into  which  stacks  of  the  cards  fitted  conveniently. 
In  the  second  compartment  from  the  right,  the  shuffled  cards  were 
stacked,  separated  into  groups  of  13  by  blank  cards.  Over  the  three 
compartments  at  the  left,  the  following  labels  were  pasted : 


The  reactor  was  required  to  take  the  cards  from  the  stack  one  at 
a  time  and  file  each  card  in  the  compartment  under  the  label  to 
which  the  syllable  on  the  card  had  the  greatest  resemblance.  For 
example,  PEL  belongs  in  the  first  compartment,  having  two  let- 
ters in  common  with  the  first  label,  only  one  in  common  with  the 
third,  and  none  in  common  with  the  second  label.  Cards  which  be- 
longed in  none  of  the  three  compartments  were  to  be  filed  in  the 
compartment  at  the  extreme  right. 

The  psychologist  took  with  a  stop-watch  the  time  for  the  sort- 
ing of  each  set  of  13  cards,  and  signaled  to  the  reactor  to  begin  a 
new  set  every  two  minutes  from  the  beginning  of  the  test.  By  using 
a  fixed  "  headway  "  in  this  way,  the  amount  of  work  done  is  uni- 
formly distributed  through  the  series. 

At  the  end  of  the  series,  the  filed  cards  were  checked  for  errors. 
Normal  and  rebreathing  series  were  taken  on  12  reactors.  In  the 
"  normal "  series,  the  reactor  sat  before  the  rebreathing  machine, 
with  the  mouthpiece  and  nose  clip  in  place,  but  breathing  normal  air. 
The  typical  results  in  one  subject,  showing  the  practice  effect,  and 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  181 

lack  of  consistent  oxygen   effect  up   to  the  beginning  of  general 
psychomotor  decline  are  presented  in  figure  5. 

2.  Tactual  discrimination. — A  test  of  tactual  discrimination  was 
carried  out  under  supervision  in  the  following  way:     Cards  were 
prepared,  each  having  a  diamond-shaped  hole  cut  in  it  in  one  of 
four  positions    (fig.  6).     The  card  rack  as  described  in  the  pre- 
ceding experiment  was  used  with  a  screen  so  arranged  that  the 
reactor  could  not  see  the  cards  nor  his  hands.    Above  each  of  four 
of  the  compartments  of  the  rack  was  fixed  one  of  the  four  types  of 
cards  and  in  view  of  the  reactor.     The  cards  to  be  sorted  were 
shuffled,  arranged  in  sets  of  20,  separated  by  blank  cards  in  the  fifth 
(right-hand)  compartment. 

The  reactor  was  required  to  take  the  cards  off  the  stack,  one  at  a 
time,  identify  them  by  feeling  them  with  the  fingers,  and  file  them 
in  the  proper  compartments.  Time  was  taken  on  the  sets,  and  subse- 
quent check  of  the  sorted  cards  made  for  errors,  as  in  the  judgment 
experiment.  "Normal"  series  on  10  men  were  conducted  with  the 
mouthpiece  and  nose  clip  of  the  rebreathing  apparatus  in  place, 
but  with  the  reactor  breathing  normal  air,  and  other  series  taken  on 
the  same  men  wrhile  rebreathing.  In  this  test  no  "headway"  was 
used,  the  reactor  commencing  on  another  series  as  soon  as  one  was 
finished.  A  typical  result  of  the  normal  and  rebreathing  series  on 
one  man  is  presented  in  figure  7. 

3.  Code  test. — A  code  test  gave  results  similar  to  the  foregoing 
tests,  except  that  in  the  reading  of  the  material  to  be  coded  adjust- 
ments of  accommodations  and  convergence  are  important,  and  dete- 
rioration in   these  functions  in   some  cases  seriously   affected  the 
results. 

8-B 

ABODE FGHIJKLMNOPQRSTUVWXYZ 
HUMCBLYESIDKNAXWPTVQROJGZF 

KXBKPGSI     ZRYULK     EHQXEGBDWV 

OI     XWTBAYKEBDEGKG 

FIG.  8. — Code  test. 

Ill  this  test,  the  codes  used,  and  the  material  to  be  coded,  were  ar- 
ranged on  a  series  of  cards  as  in  figure  8,  and  these  cards  were  pre- 
sented in  succession  to  the  reactor,  who  was  required  to  write  the 
coded  message  in  the  lower  part  of  the  card. 

4.  Dynamometer     test.— In  order  to  find  the  effect  of  asphyxia- 
tion on  the  muscular  force  capable  of  exertion  by  limited  systems,  a 
series  of  dynamometer  tests  were  run  through.     In  these  tests,  the 
reactor  was  required  to  exert  his  maximal  effort  on  a  hand  dyna- 


182  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

mometer  every  two  minutes.  Normal  and  rebreathing  series  were 
taken  on  10  reactors.  Typical  results  on  one  reactor  are  presented 
in  figure  9. 

5.  Handwriting. — In  order  to  measure  the  effect  of  oxygen  hun- 
ger at  different  barometric  pressures,  and  the  completeness  of  the 
restoration  process  attained  by  the  administration  of  oxygen,  a  sim- 
ple handwriting  test  was  devised  and  carried  out  in  the  low-pressure 
chamber.  A  standard  psychological  vocabulary  test  of  100  words 
was-  used  in  making  up  the  test  cards.  The  100  words  of  the 
standard  vocabulary  test  were  cut  up  and  put  in  a  hat  and  shuffled. 
As  the  words  were  drawn  from  the  hat  they  were  typewritten  on 
a  standard  library  card.  By  this  method  three  test  cards  of  100 
words  each  were  obtained.  The  task  of  copying  these  cards  offered 
the  same  difficulty  to  the  subject  since  the  same  words  were  used  on 
each  test  card  only  the  order  being  different.  Since  the  copying 
of  words  is  an  old-established  habit,  there  was  little  improvement 
through  practice. 

The  test  was  carried  out  as  follows : 

The  subject  was  seated  at  a  table  in  the  tank.  On  a  given  signal 
the  motor  of  the  tank  was  started,  but  the  pressure  was  not  changed. 
The  subject  was  handed  card  No.  1  and  was  asked  to  copy  it  as 
neatly,  as  rapidly,  and  as  accurately  as  he  could.  As  soon  as  this 
task  was  completed,  the  time  of  writing  the  card  was  taken.  (This 
gives  the  normal  record.)  The  signal  for  ascent  (decrease  in  pres- 
sure) was  then  given.  The  ascent  was  made  at  the  rate  of  about  1,000 
feet  per  minute.  After  the  subject  had  reached  the  given  height 
he  was  kept  at  that  level  for  15  minutes  with  the  motor  running  (to 
keep  the  noise  constant).  At  the  end  of  the  15-minute  period  at 
the  given  height  the  subject  was  asked  to  copy  the  second  test  card. 
After  completing  the  copying,  his  time  was  taken  as  before.  (This 
gives  the  oxygen-hunger  record.)  The  subject  was  then  given  oxy- 
gen for  two  minutes  and  was  then  asked  to  copy  the  third  test  card. 
(This  gives  the  oxygen-restoration  record.)  Upon  the  completion 
of  the  latter,  the  signal  for  descent  was  given. 

The  results  from  these  handwriting  tests  were  then  treated  as 
follows:  First,  they  were  measured  (with  reference  to  general  form 
and  legibility)  on  the  scale  for  handwriting.  This  scale,  as  is  well 
known,  enables  one  directly  to  measure  the  quality  of  a  given  hand- 
writing production  in  terms  of  certain  units.  For  example,  his 
normal  might  correspond  to  unit  12  on  the  scale ;  his  oxygen-hunger 
record  might  correspond  to  unit  8  on  the  scale. 

In  rating  the  tests  on  the  various  subjects  a  penalty  of  20  was 
attached  for  each  unit  lost  on  the  scale.  In  addition  to  this  rating 
on  the  scale,  the  following  penalties  were  also  imposed : 


CAPT.   BORING.      (Fig.   lOa.) 
Handwriting,  standard  card — normal.     14,000  ft. 


CAPT.   BORING.      (Fig.   lOb.) 
Handwriting,  standard  card — oxygen  hunger.     14,000  ft. 


..,  .JT=O.  (juJLuA*. 
1 

fy..O»Aj_X_A,-J    •  *  / 
<i~~ *J 


jJU^j*^    ,l 

,     -^\     g 


CAPT.  BORING.      (Fig.   lOc.) 
Handwriting,  standard  card — oxygen  restoration.     14,000  ft. 


J./  sr     / 

? s .'/  i  {.f  A *•**(.«. H*"- <*4 1-' 
c 'j£*t  /<#*  -.  f  ^  i  <"«/<  /P 


183-1 


PVT.  WICKMAN.      (Fig.  lla.) 
Handwriting,  standard  card — normal.     18,000  ft. 


PVT.  WICKMAN.      (Fig.  lib.) 
Handwriting,  standard  card — oxygen  hunger.     18,000  ft 


(.-t-  '-   ((  i  cL^-^t^ 

V'          -'-<A/l  fc-cJ  ?. 


PVT.   WICKMAN.      (Fig.   lie.) 
Handwriting,  standard  card — oxygen  restoration.     18,000  ft. 


Mil^^^^'^^ 
'<"*>* 


,  y   s    't&KLeh,  rs>  /'/Ti^¥'z^^r//^^^/^r'**/^'r 

£4**6*  A  tiftttZ}S*&£*(*&t Z^3r(**4&'&tev&fc 
*^&%^^ 


183-2 


CAPT.   DAVIS.      (Fig.    12a.) 
Handwriting,  standard  card — normal,  22,000  ft. 


CAPT.   DAVIS.      (Fig.    12b.) 
Handwriting,  standard  card — under  oxygen  hunger.     22,000  ft. 


V  J\Q> 
1       f 

.(-V 
• 


CAPT.  DAVIS.      (Fig.   12c.) 
Handwriting,    standard   card — oxygen    restoration.      22,000    ft. 


< . 


183-3 


MANUAL   OF    MEDICAL  RESEAECH   LABORATORY. 


183 


For  each  word  omitted,  a  penalty  of  2. 

For  each  word  misspelled  or  wrong  word  used,  a  penalty  of  2. 

For  each  word  crossed  out  and  rewritten,  a  penalty  of  2. 

For  each  word  careted  in,  a  penalty  of  2. 

For  each  word  or  letter  thereof  written  over,  a  penalty  of  2 

each  word. 

Failure  to  follow  line  as  well  as  original,  a  penalty  of  2. 
For  each  10  seconds'  increase  in  time  over  the  normal,  a  pen- 
alty of  1. 
For  each  10  seconds'  decrease  in  the  time  of  writing,  a  credit 

of  1  was  given. 

It  will  thus  be  seen  that  errors  in  the  normal  are  estimated  as  well 
as  those  made  under  oxygen  hunger  or  after  oxygen  administration. 
A  typical  record  follows: 

Record  of  Pvt.  Wickman,  altitude  18,000  feet. 


Normal. 

Under 
oxygen 
hunger. 

Two 
minutes 
after  ad- 
ministra- 
tion of 
oxygen. 

Legibility  rated  on  scale,  last  8  lines  only  (penalty  of  20  for  each  unit  lost 
on  scale:  credit  of  20  for  each  unit  gained)  . 

0 

—    80 

0 

Word  omitted  (penalty  of  2  each  word)  

0 

—    12 

0 

Word  mispelled  or  wrong  word  used  (penalty  of  2  each  word)  

—  2 

0 

Word  scratched  out  and  rewritten  (penalty  of  2  each  word)  . 

0 

_      2 

o 

Word  careted  in  (penaltv  of  2  each  word)  

0 

0 

Wnrd  (or  any  part  thereof  written  over,  penaltv  of  2  each  wordl 

....  4 

—      6 

o 

P'ailure  to  follow  line  as  well  as  original  (penalty  of  2  each  line  on  last  8 
lines)  

0 

0 

Time,  penalize  1  for  each  10  seconds  increase  or  credit  1  for  each  10  seconds 
decrease  

0 

+  3 

Total  penalties  or  credits  

—  6 

—  100 

+  3 

These  tests  have  been  made  at  14,000  feet,  16,000  feet,  18,000  feet, 
and  22,000  feet.  While  complete  records  are  not  in,  the  results  so 
far  obtained  show  that  at  14,000  feet  the  effect  of  oxygen  hunger  is 
exceedingly  slight  (see  fig.  10)  ;  at  16,000  feet  the  effect  is  scarcely 
more  noticeable;  while  at  18,000  feet,  on  some  subjects,  at  least, 
the  effect  is  extremely  marked  (see  fig.  11,  the  same  subject).  The 
handwriting — in  some  cases — becomes  difficult  to  read,  whereas  other 
errors  in  spacing,  following  the  line,  omission  of  words,  etc.,  are 
very  marked.  At  22,000  feet  the  first  two  subjects  fainted,  and  it 
was  not  possible  to  continue  the  experiment.  So  far  only  one  record 
has  been  obtained  at  22,000  feet  (fig.  12).1 

In  every  case,  except  those  where  heart  dilatation  and  fainting 
occurred,  the  2  minutes'  administration  of  oxygen  completely  re- 
stored the  handwriting  to  normal. 

1  It  should  be  noted  that  the  altitudes  are  given  by  altimeter  readings,  and  should  be 
considerably  increased  if  allowance  is  made  for  the  difference  in  temperature  of  the  air 
in  the  tank  and  that  corresponding  to  the  same  pressures  in  the  upper  atmosphere. 


184  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

It  was  planned  to  continue  this  experiment  by  the  same  method 
with  the  machine-gun  camera  and  with  a  telegraph  recording  outfit, 
and  to  obtain  and  contrast  a  similar  set  of  records  on  the  rebreath- 
ing  tank  and  the  refrigerated  pressure  chamber.  It  was  thought 
that  the  results  on  the  handwriting  test,  the  machine-gun  camera, 
and  the  recording  telegraph  would  give  a  tangible  picture  to  the 
aviator  of  just  what  difficulties  he  would  meet  with  in  the  air  in 
writing  messages,  in  sending  them,  and  in  the  accuracy  of  his  ma- 
chine-gun work,  and  how  these  difficulties  could  be  overcome  by  the 
use  of  oxygen. 

6.  Memory. — Various  tests  on  memory  were  employed.  For  im- 
mediate memory,  series  of  from  5  to  12  consonants  are  numbered, 
and  series  of  from  2  to  5  observations,  each  made  up  of  a  color  name 
and  a  number,  were  employed.  Samples  of  the  consonant  series  and 
observation  series  are  given  below : 

RKZWT 

CXWNZF 

JLXBRVN 

NHBDZVCR 

VJSRBLTMW 

HRKGWMDPTL 

ZXWKDTNVSHQ 

YPCQDKWZMTBJ 

The  observation  series  were  made  up  in  pairs  of  series,  the  same 
color  name  not  occurring  in  both  series,  and  in  the  tests  the  two 
members  of  a  pair  were  given  in  succession,  in  order  to  avoid 
confusion  between  successive  series. 

The  "  observation  tests  "  were  especially  satisfactory  as  tests  and 
may  be  used  successfully  where  immediate  memory  tests  are  required. 
Neither  test,  however,  showed  any  deterioration  in  immediate  mem- 
ory due  to  asphyxiation. 

a.  b. 

white 63  ecru 81 

russet 84  black 52 

gray 47  green 24 

amber 28  lilac 73 

violet 96  orange 35 

red 58  blue 74 

tan 14  buff 29 

gold 85  rose 95 

azure 46  drab 62 

yellow 69  purple 79 

scarlet 57  crimson 13 

Btraw 25  slate 68 

brown 18  pink 37 

lavender 36  indigo 92 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  185 

For  visual  memory  the  position  memory  board  (fig.  B)  was  used. 
This  board  has  mounted  in  a  vertical  plane  49  miniature  lamps 
arranged  in  a  square  pattern,  the  individual  lamps  3  inches  apart, 
vertically  and  horizontally.  By  means  of  a  plug  board  and  master 
key  behind  the  board  any  number  of  lights  from  1  to  14  can  be 
lighted  simultaneously  in  any  chosen  position.  In  practice  the 
reactor  was  shown  from  three  to  seven  lights  for  three  seconds,  and 
then  required  to  chart  the  positions  on  a  printed  form  (fig.  14). 
The  lights  were  presented  before  or  during  the  rebreathing  test,  and 
the  charting  was  done  immediately,  or  after  a  short  or  long  interval. 
While  no  effects  of  asphyxiation  were  demonstrable  up  to  the  time 
at  which  the  marking  of  the  chart  became  impossible  on  account  of 
disturbance  of  motor  control,  the  method  appears  valuable  for  other 
than  the  rating  work. 

7.  Mathematical  tests. — Several  mathematical  tests  were  employed, 
the  most  satisfactory  being  the  attention  test.     In  this  test  two 
sheets,  each  containing  16  lines  of  45  digits  each,  were  used.    Each 
of  the  32  lines  of  digits  was  carefully  made  up  so  that  the  lines 
two  sheets,  each  containing  16  lines  of  45  digits  each,  were  used. 
Each  of  the  32  lines  of  digits  was  carefully  made  up  so  that  the  lines 
presented  equal  difficulty.     Before  commencing  the  test  a  standard 
number  of  12,  13,.  14,  or  15  was  written  before  each  line  and  the 
reactor  required  to  add  the  digits  in  each  line,  beginning  at  the  left, 
until  the  progressing  sum  equaled  the  standard  number  or  one  over 
that  number,  drawing  in  each  case  a  line  between  the  last  digit  of  the 
group  added  and  the  next  digit  and  writing  the  difference,  if  any. 
between  the  sum  of  the  group  and  the  standard  number  over  the 
group.    By  changing  the  order  of  the  standard  number,  128  lines  are 
available.    A  typical  sheet  of  this  test  is  shown  in  figure  15. 

This  test  showed  no  definite  asphyxiation  effects  prior  to  the  period 
of  general  psychomotor  decline,  and  is  affected  somewhat  by  eye  con- 
ditions and  practice  effects.  It  has  shown  possibilities  of  advan- 
tageous use  for  other  practical  purposes,  however,  and  work  will  be 
continued  with  it. 

8.  Auditory  tests. — Tests  on  the  sensitivity  and  acuity  of  the  vari- 
ous sense  organs.    By  using  brief  tests  which  permit  the  attainment 
of  "attention  peaks,"  it  is  demonstrable  that  the  efficiency  of  the 
various  sensory  mechanisms  does  not  show  appreciable  deterioration 
until  the  general  psychophysical  breakdown.    Our  detailed  work  has 
been  principally  on  auditory  efficiency,  with  some  work  on  visual 
efficiency  done  before  the  ophthalmological  section  was  organized. 

Tests  on  the  range  of  auditory  perception  of  12  reactors,  with  a  set 
of  22  steel  cylinders,  with  range  up  to  32,000  vibrations  (fig.  16), 
showed  no  difference  between  normal  and  rebreathing  series  up 
to  the  point  of  general  psychomotor  inefficiency.  Tests  with  the 


186  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

acumeter  (fig.  17)  for  sensitivity  to  the  note  of  256  vibrations  are 
at  present  being  carried  on,  and  so  far  indicate  no  consistent  deteriora- 
tion of  sensitivity  until  the  late  stages  of  asphyxiation.  In  other 
words,  the  reactor  can  hear  as  faint  a  sound,  up  to  a  late  stage  of 
asphyxiation,  as  he  can  in  normal  condition  if  his  attention  is  good 
at  the  moment  of  listening.  As  has  been  previously  explained,  the 
"  attention  peaks  "  can  be  evoked  even  in  relatively  late  stages  of 
asphyxiation  if  the  experiment  is  conducted  by  the  methods  usually 
employed  by  trained  psychologists. 

9.  Continuous  reaction. — The  continuous-reaction  board  (fig.  18) 
which  was  used  in  one  of  our  early  tests,  and  which  was,  as  a  matter 
of  fact,  the  starting  point  from  which  our  final  apparatus  for  the 
rating  tests  (LVN  apparatus)  was  developed,  could  not  be  used  for 
rating  work  because  of  the  rapid  but  variable  improvement  with 
practice  in  its  manipulation.  In  this  apparatus  24  miniature  lights 
are  arranged  in  a  circle,  with  a  two-way  switch  at  the  base  of  each. 
By  a  master  switch,  a  lamp  is  lighted ;  the  reactor  is  required  to  turn 
off  each  lamp  as  soon  as  it  lights  by  moving  the  appropriate  switch ; 
the  turning  off  of  one  lamp  turns  on  another  at  some  point  in  the 
semicircle  determined  by  the  previously  arranged  interconnection  of 
a  switchboard  concealed  within  the  apparatus  so  that  the  reaction  is  a 
continuous  one  until  the  twenty-fourth  lamp  has  been  turned  out,  or 
may  be  continued  through  a  longer  period. 

IV.  FURTHER  PSrCHOLOGICAL  INVESTIGATIONS  OF  PROBLEMS  OF  AVIATION. 

1.  Decrease  of  after-nystagmus  times  with  successive  rotations. — 
The  importance  assigned,  in  the  examination  of  aviators,  to  certain 
ocular  movements  which  follow  upon  rotatory  movements  of  the  head 
and  body  has  suggested  an  experimental  investigation  into  the  effect 
upon  these  ocular  movements  of  rotations  continued  for  several  days 
or  weeks  together.  Experiments  have  made  it  apparent  that  under 
certain  circumstances  persistent  rotation  in  the  clinical  revolving 
chair  leads  to  a  considerable  reduction  in  the  violence  and  the  dura- 
tion of  these  characteristic  ocular  movements.  In  one  case  the  dura- 
tion of  the  after-nystagmus,  e.  g.,  as  observed  during  May,  1918,  fell 
from  about  25  seconds  to  11  seconds  after  several  daily  series  lasting 
vfor  a  few  minutes  a  day  at  a  constant  rate  of  one  revolution  in  2 
seconds. 

Further  to  investigate  the  effect  of  repetition  upon  ocular  move- 
ments, six  enlisted  men  were  turned  ten  times  a  day  (five  times  right 
and  five  times  left)  between  June  6  and  July  13,  1918.  Two  of  the 
men  were  begun  later  than  the  others  and  intervals  of  one  or  more 
days  interrupted  here  and  there  the  continuity  of  the  diurnal  trials. 
The  results  are  given  in  the  accompanying  Table  I  (fig.  19)  and  chart. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 
TABLE  I. 


187 


Brown. 

Caplan. 

Ratull. 

Stewart. 

Wichmann. 

Ackermann  . 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

June    6 
7 
s 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 

R 

26.6 
27.6 
27.2 
27.0 

1.9 
1.7 
2.2 
1.6 

23.2 
29.4 
27.6 
25.0 

2.6 
2.5 
3.9 

2.8 

22.2 
20.6 
22.8 
20.0 

2.2 

1.5 
2.2 

.8 

24.3 
25.6 
22.0 
28.0 

6.7 
1.5 
4.0 
3.0 

1-5... 
6-10 



R 

L 

1  5 

6-10 

R 

22.3 

2.9 

20.  X 

1.4 

22.0 

?  6 

L  

1  5 

25.0 
24.0 

2.0 
4.0 

20.2 
21.6 

3.4 
2.3 

23.6 
19.7 

3.1 
.9 



6-10 

16.7 

4.3 

19.4 

2.7 

26.0 

1.3 

R 

* 

L 

1-5 

6-10 

R 

20  2 

.6 

19.6 

1  9 

20  2 

3.4 

L  
1-5  
6-10  

R 

21.4 
21.0 
20.6 

1.3 
1.6 
.5 

23.0 
22.2 
20.2 

14.5 

1.2 
2.0 
2.2 

1  3 

19.0 
20.6 
18.6 

15  0 

3.6 
2.9 
3.4 

2.4 

17.6 

2.1 

:::::: 

L  
1-5  

6-10 

20.0 
17.5 
16.5 

17.0 

1.3 
2.5 
2.5 

2.0 

13.4 
17.0 
11.2 

15.8 

3.0 
2.8 
1.4 

1.4 

17.0 
19.2 
15.4 

16.4 

2.4 
1.4 
1.7 

1.9 

R 

22.0 

2.8 

28.0 

5.2 

L.. 

22.8 

2.2 

20.7 

1.8 

13.8 

2.2 

16.0 

1.6 

28.0 

4.0 

1-5 

21.4 

2.9 

18.3 

2  8 

16.0 

1.2 

17.0 

1.8 

32.2 

5.6 

6-10  
R... 

23.4 

1.9 

17.5 

2.3 

13.6 

12.8 
11.4 

2.1 

1.7 
2.3 

15.4 

14.0 
14.4 

1.5 

4.0 
1.5 

23.8 

28.6 
29.4 

2.6 

2.1 
4.7 

L.. 

1-5  

13.6 
10.6 

1.9 

1.7 

16.6 
11.8 

2.1 
1.8 

31.8 
26.2 

2.2 
3.0 

6-10 

R... 
L 

18.0 
16.8 

1.6 
1.4 

14.2 
19.2 

.6 
1.8 

12.4 
11.0 

1.5 
1.2 

9.6 
9.2 

1.7 
1.7 

23.4 

24.6 

2.0 
1.3 

1-5     

18.6 

1.1 

17.0 

2.8 

13.2 

.7 

10.8 

.6 

25.4 

.7 

6-10 

16.2 

1.4 

16.4 

2.5 

10.2 

.6 

8.0 

.8 

22.6 

1.3 

R... 

14.2 
15.0 

2.6 
2.0 

10.8 
10.6 

1.0 

1.5 

6.8 

7.8 

1.0 
.9 

L 

1-5 

15.2 
14.0 

3.0 
1.6 

11.6 
9.8 

1.3 

.6 

6.6 
8.0 

.9 

.8 

6-10  

R... 

L  

1-5 

6-10  

R... 
L  

1-5     .. 

24.4 
21.8 
22.6 

2.7 
3.4 
2.5 

13.0 
18.0 
16.0 

3.0 
1.0 
.0 

:::::: 

8.8 
9.8 
10.8 

1.8 
1.5 
1.0 

27.6 
29.0 
27.4 

2.7 
1.6 
2.1 

6-10  

23.6 

4.5 

15.0 

14.4 
16.2 
15.6 
15.0 

14.8 
15.2 
16.4 
13.6 

11.4 
11.4 
12.0 
10.8 

5.0 

1.5 
1.6 
1.1 

2.0 

2.6 
1.4 
1.7 
2.5 

1.1 
.9 

.8 
.6 

7.8 

1.4 

29.2 

2.2 

R..., 
L  
1-5  

14.2 
12.8 
14.0 
13.0 

14.8 
13.4 
15.2 
13.0 

13.4 
11.0 
14.0 
10.4 

2.6 
2.4 
2.8 
2.4 

2.2 
.9 
1.8 
.4 

1.8 
2.0 
1.6 
1.3 

10.8 
10.0 
12.0 
8.8 

7.6 
7.8 
8.2 
7.2 

5.6 
5.0 
6.6 
4.0 

2.1 
2.0 
2.0 

.7 

.5 
1.4 
.6 
.6 

1.5 
1.2 
.9 
.0 

23.2 
22.8 
24.6 
21.4 

23.6 
23.6 
23.6 
23.6 

19.0 
22.2 
21.6 
19.6 

2.2 
1.8 
2.1 

.7 

1.9 
2.5 
2.5 
1.9 

2.0 
1.4 
1.3 
2  5 

...... 

6-10  

R..., 
L  

18.4 
16.2 
18.0 
16.0 

2.1 
1.4 
1.9 
1.2 



1-5 

6-10  

R... 
L  
1-5  
6-10  





R.... 
L  
1-5  
6-10  

15.2 
13.4 
14.6 
14.0 

1.0 
.5 
1.3 

.8 

9.4 
11.2 
10.2 
10.4 

.7 
1.0 
1.0 
1.3 

7.2 

7.8 
7.6 
7.4 

.6 
.6 
.9 
.5 

1.6 
1.0 
2.6 
.0 

1.9 
1.6 
1.0 
.0 

15.8 
17.2 
17.0 
16.0 

1.4 
2.6 
2.4 
2.4 





188  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

TABLE  I — Continued. 


Brown. 

Caplan. 

Rahill. 

Stewart. 

Wichmann. 

Ackermartn. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

June  22 
23 
24 
25 
26 
27 
28 
29 
30 

July    i 

2 
3 
4 
5 

6 
7 

R... 
L  



10.0 
10.8 

.8 
1.7 





5.4 
2.2 

.9 

1.7 

17.0 
18.8 

2.4 
2  2 





1-5  

10.2 

.7 

4.8 

1.4 

18.8 

1  9 

6-10  
R... 





10.6 

1.8 



2.8 

1.1 

17.0 

2.4 





L  

1-5  

6-10  

R  
L  
1-5  
6-10  

R... 
L  
1-5  
6-10  

R... 
L  

11.6 
11.2 
11.8 
11.0 

10.8 
9.4 

1.5 
1.0 
1.0 
1.2 

1.4 
.5 

7.0 
8.4 
8.0 
7.4 

7.8 
8.2 
8.4 

7.8 

6.6 
8.6 

1.2 
1.5 

.8 
2.4 

1.0 
1.0 
1.1 
1.2 

1.3 

2.5 

7.6 
7.2 
8.6 
6.2 

7.6 
6.6 
2.3 
1.7 

8.6 
6.8 

2.1 
1.8 
1.4 
1.8 

2.3 

1.7 
1.5 

1.7 

.5 
1.0 

1.4 

.6 
1.2 

.8 

.0 
.0 
.0 
.0 

.0 
.0 

1.4 
.9 
.8 
.5 

.0 
.0 
.0 
.0 

.0 
.0 

15.0 
16.0 
16.4 
14.6 

12.8 
14.2 
15.4 
11.6 

10.4 

10.8 

2.0 
2.4 
1.3 
2.3 

2.2 
1.8 
1.9 
1.3 

1.7 

1.4 

-•-• 

"'--•" 

1-5  
6-10  

R.. 

10.8 
9.4 

1.4 
.7 

8.2 
7.0 

2.2 
2.0 

7.4 
8.0 

1.1 

.8 

.0 

.0 

.0 
.0 

11.4 

9.8 

1.5 

2.2 

29.4 
31.2 
31.4 
29.2 

23.4 

29.8 
25.2 
26.0 

21.6 
22.6 
20.6 
16.6 

2.3 
2.6 
2.3 
3.0 

1.3 
1.0 

1.8 
2.4 

1.1 
2.1 
3.3 
1.9 

L  

1-5  

6-10  

R.. 

L  

1-5  

6-10  

R... 

L  

1-5  

6-10  

R... 

L  

1-5  

6-10  

R... 

14  8 

1.8 

10.4 

1.9 

.... 

20.8 
23.4 
24.0 
20.2 

17.8 
18.4 
17.4 
18.0 

14.2 
13.6 
14.2 
13.6 

1.4 
2.9 
2  4 
1.0 

3.6 
1.1 
2.1 
2.2 

3.4 
1.9 
3.8 
1.5 

18.2 
19.0 
20.6 
16.6 

14.2 
16.8 
16.4 
14.6 

15.8 
15.2 
16.2 
14.8 

2.6 
3.2 
3.3 
1.9 

1.9 
1.4 
2.7 
1.3 

1.8 
1.2 
1.4 
1.4 

L  

14.4 

1.7 

7.4 

2.5 

1-5  

13.0 

1.2 

7.6 

2.5 

6-10  

R... 
L  

16.2 

15.4 
14.8 

1.0 

.5 

.7 

10.2 

6.0 
6.0 

1.4 

1.6 
.8 





1-5  
6-10  

15.2 
15.0 

.3 
.1 



6.8 
5.2 

1.0 
1.4 



R... 

13  4 

1  5 

L  

13  8 

1  1 

1-5  

14.2 

1.0 

6-10...  . 

13  0 

1  6 

R 

L    

1-5   ' 

6-10     

R 

8.4 

1.3 

17.4 
15.2 
15.4 
17.2 

13.0 
14.2 
14.0 
13.2 

2.3 
2.2 
2.5 
2.2 

1.6 
.3 
1.2 
1.0 

13.2 
14.4 
13.8 
13.8 

12.0 
14.6 
13.0 
13.6 

1.4 
.9 
1.0 
1.4 

1.2 
.5 
1.2 
1.4 

L  
1-5  
6-10  





6.8 
8.8 
6.4 

1.0 
1.0 
.9 

R... 

8.4 

.7 

L  

6.2 

1.0 

1-5 

8  2 

g 

6-10 

6  4 

1.3 

R 

L    

1-5 

6-10... 



MANUAL  OF   MEDICAL  RESEARCH  LABORATORY. 
TABLE  I — Continued. 


189 


Brown. 

Caplan. 

Rahill. 

Stewart. 

Wichmann. 

Ackermann. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

Av. 

M.V. 

July     8 
9 
9 
10 
l! 

13 

14 
15 
16 
17 
18 

R... 
L 

18.0 
16.4 

2.0 
1.9 

12.6 

10.6 

1.3 
1.9 

18.4 
17.0 
17.4 
18.0 

11.8 
10.6 
12.0 
10.6 

2.1 
.4 

1.8 
4.0 

1.8 
1.4 
1.6 
1.5 

12.2 
12.2 
12.2 
12.2 

10.8 
12.4 
12.6 
10.6 

8.2 
8.2 
8.8 
7.6 

11.0 
9.8 

2.2 
1.0 
2.2 
1.0 

1.4 
1.1 
.9 
1.3 

1.0 
1.0 
1.0 
.7 

.4 
1.0 
.8 
1.0 

1.3 
1.1 
.9 
1.3 

.5 
.4 
.4 
.6 

1  5 

1  5              

15.8 

1.8 

13.4 

.5 

6-10 

18.6 
13  4 

1.5 
1.9 

9  8 
10.6 

1.0 
1.3 

R 

L  
1-5  
6-10  

R 

11.6 
14.6 
10.4 

1.9 
.9 
.9 

9  4 
10.2 
8.8 

.9 
1.1 

.6 

...... 

L 

1  5 

6-10              

R 

9.2 
9  8 

1.8 
2.6 

I, 

1-5 

8.4 
10.6 

1.7 
2.3 

10.0 
10.8 

9.6 
8.4 
9.6 
8.4 

9.2 
9.0 
9.4 

8.8 

7  6 

6-10                .   . 

R 

9.6 

.9 

L 

9  0 

.4 

1-5 

10  0 

.4 

6-10            .  .  . 

8  6 

.5 

R 

8.6 

.8 

L    

8.2 

.3 

1-5  

8.8 

.6 

6-10  

8.0 

.4 

R 

7  2 

.3 

L.      ... 

6  8 

.6 

6.8 
7.8 

.6 
1  3 

1-5  

7  2 

.6 

6-10           

6.8 

.3 

6.6 

.9 

R... 

L  

1-5  

6-10           .... 

R.. 

6.4 
6.6 
6.6 
6.4 

.5 
.7 
.7 
.5 

L  

1-5  

6-10  

R... 

L  

1-5  

6-10  

R... 

'" 

7.6 
7.2 
7.6 

.5 
.3 

5 

L  

1-5  

6-10  

7.2 

.-3 

R.... 

L  

1-5  

6-10  

The  method  of  observation  and  record  *  was  improved  (1)  by  timing 
the  rotatory  movement  of  the  chair  with  the  sound  of  a  seconds'  met- 

1  In  adopting  a  definite  standard  technique  for  the  conduct  of  a  large  number  of  ex- 
aminations to  be  held  at  scattered  stations  by  many  examiners  under  varying  conditions, 
the  use  of  complicated  instruments  of  precision  is,  of  course,  neither  necessary  nor 
practicable.  Intervals  of  a  day  or  more  between  turnings  were  sometimes  inevitable  owing 
to  the  military  duties  of  the  men  examined.  It  will  be  noted  that  there  occurs  quite  a 
variation  in  the  readings  from  day  to  day.  This  may  be  due  to  slight  variation  in  the 
stimulation  employed  or  to  inaccuracies  in  reading  the  nystagmus.  The  former  factor 
was  overcome  as  far  as  possible  by  timing  the  rate  of  turning  with  a  stopwatch,  while 
the  latter  was  minimized  by  having  all  the  readings  taken  by  one  observer.  These 
variations,  however,  do  not  vitiate  the  main  results  as  stated  above. 


190  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

ronome  used  to  replace  a  stop  watch  and  (2)  by  recording  the  later 
phases  of  nystagmus  upon  a  revolving  drum  with  time  marker. 
Jacquet  seconds  clock,  and  telegrapher's  key.  The  auditory-kinaes- 
thetic  rhythm  incited  by  the  metronome  forms  a  much  more  natural 
and  accurate  control  for  the  rotation  of  the  chair  than  the  stop  watch, 
and  the  graphic  record  of  eye  movements  eliminates  the  double  error 
of  anticipating  and  delaying  the  cessation  of  nystagmus,  an  error 
inherent  in  the  single  movement  of  the  thumb  or  finger  upon  the  stem 
of  the  watch.  This  double  error  may  amount  to  several  seconds.  The 
usual  stop-watch  method  offers  no  means  of  control  over  the  variable 
errors  of  expectation  and  habituation  and  the  constant  errors  of  time. 
All  of  these  errors  are,  of  course,  scrupulously  calculated  in  any  rec- 
ognized method  of  science. 

These  experiments  were  conducted  by  assistants  in  the  laboratory. 
From  time  to  time  the  method  was  inspected,  and  occasional  readings 
were  made  of  after-nystagmus  with  the  stop  watch.  In  the  table  each 
average  time  for  5  right  turns  and  5  left  turns  is  given,  as  well  as 
the  average  of  the  first  5  and  the  last  5  turns  in  each  series.  Mean 
variations  are  calculated  in  each  case.  In  every  instance  the  rate  was 
10  turns  in  20  seconds.  Intervals  of  two  minutes  (between  right  and 
left)  and  three  minutes  (between  pairs)  were  observed.  In  a  few 
cases  the  regular  series  was  interrupted  or  shortened  by  severe  organic 
disturbances  revealed  by  nausea,  qualmishness,  pallor,  excessive  respi- 
ration, and  general  distress. 

The  results  bear  evidence  of  the  decline  of  the  duration  of  after- 
nystagmus  (1)  from  day  to  day  and  (2)  from  trial  to  trial  within  a 
single  period  of  experimentation. 

The  average  times  for  the  four  observers  who  began  on  June  6  run 
as  follows  from  day  to  day : 

Seconds.  Seconds. 

June  6 24.  9     June  18 13.  0 

8 22.3  19 13.5 

10 20.  6  20 9.  6 

11 16.2  21 8.3 

12 18.  0  22 7. 1 

13 13.6  24 6.8 

1.4 13. 8  25 5.  0 

15 10.  8  26 6.  3 

17 15.  9 

In  20  days,  then,  the  decrease  in  time  exceeds  18  seconds  (24.9—6.3 
seconds).  The  drop  in  time  is  fairly  consistent  in  spite  of  the  fact 
that  it  proved  to  be  impossible  to  arrange,  without  exception,  the 
daily  program.  The  temporal  decline  is  graphically  expressed  in  the 
chart,  which  is  based  upon  the  nystagmus  for  the  first,  fifth,  tenth, 
and  fifteenth  turning  days,  regardless  of  calendar  dates,  for  all  six 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  191 

subjects.  The  initial  times  for  all  subjects  fell  within  22-31  seconds; 
and  they  decline  at  somewhat  unequal  intervals  for  the  different  men. 
The  total  range  of  decline  expressed  in  whole  numbers  for  the  first 
10  days  stood  as  follows : 


Subject  A 30—12=18  seconds 

Subject  B 27—10=17  seconds 

Subject  C__          _  26—11=15  seconds 


Subject  R 21—14=  7  seconds 

Subject  S 25—  8=17  seconds 

Subject  W  _.         _  28—15=13  seconds 


The  difference  is  not  very  great,  save  in  the  case  of  R,  whose  times 
were  least  shortened  within  this  limited  time.  R  dropped  sharply 
(14  to  8  seconds),  however,  within  the  next  five  days,  while  S  fell 
off  to  zero. 

To  revert  to  the  decrease  in  time  of  the  ocular  movements  during 
the  period  of  experimentation  each  day,  the  times  nearly  always 
decline  during  the  10  trials,  as  in  the  case  of  the  May  experiments 
made  upon  the  single  subject.  The  few  negative  cases  are  significant. 
The  most  striking  case  appears  in  S's  first  two  days.  On  these  two 
days  the  subject  became  so  violently  nauseated  that  the  trials  had  to 
be  broken  off  after  the  sixth  turn.  Thereafter  the  ocular  movements 
grew,  from  day  to  day,  much  less  violent  and  of  smaller  excursion, 
qualmishness  disappeared,  and  the  nystagmus  rapidly  lessened  in 
duration.  All  of  the  other  negative  cases  of  more  than  a  second  or 
so  occurred  just  after  two  or  more  blank  days  and  they  fell  in  with 
an  absolute  increase  in  nystagmus  time,  and  usually  with  a  greater 
violence  in  the  general  organic  effects  of  rotation.  These  blank  days 
were  coincident  with  holiday  leaves  for  the  subjects  during  which 
their  daily  routine  was  interrupted.  The  disturbance  of  routine  may 
very  well  have  led  to  a  physiological  disturbance  producing  a  cumu- 
lative effect  and  masking  the  usual  decline  during  the  last  half  of  the 
period. 

It  seemed  altogether  probable  that  the  change  of  after-nystagmus, 
which  occurred  not  only  from  turn  to  turn,  but  also  from  day  to  day, 
should  be  a  function  of  elapsed  time  as  well  as  of  repetition.  The. 
accompanying  table  (II)  gives  the  relative  frequency  of  increase 
and  decrease  in  after-nystagmus  after  intervals  and  immediately 
after  turning  days.  The  totals  for  all  subjects  suggest  that  the  blank 
clays  retard  the  gradual  decline  to  which  attention  has  been  called. 
But  a  scrutiny  of  the  table  will  make  it  apparent  that  virtually  all 
the  positive  evidence  is  confined  to  the  figures  for  the  last  two  sub- 
jects (R.  and  W.),  who  also  reported  an  increased  violence  in  the 
apparent  visual  movements  and  in  organic  disturbances  after  in- 
tervals of  rest. 


192  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

TABLE  II. 


After  interval. 

After  no  interval. 

Increases. 

Decreases. 

Increases. 

Decreases. 

Ackerman          

1 
1 
2 

9 

5 
12 
7 
6 
5 
2 

3 
2 

7 
4 
6 
6 

16 
4 
13 
1C 
24 
22 

Brown  

Caplan  

Stewart  

Rahill             

Wichmami  

Total  

29 

37 

28 

95 

It  is  impossible,  then,  to  generalize  upon  the  effect  of  time  interval. 
Repetition  of  turning  certainly  leads,  under  certain  circumstances, 
to  a  decrease  in  after-nystagmus.  But  that  the  decline  depends  in 
any  fixed  way  upon  the  length  of  the  temporal  interval  can  not  be 
maintained  upon  the  basis  of  the  evidence  at  hand.  The  decline  is 
not  to  be  laid  to  a  simple  process  of  adaptation  in  the  receptor  organs 
of  the  labyrinth,  for  such  sensory  adaptations  as  are  best  known- 
visual,  tactual,  and  thermal — are  of  brief  duration,  and,  furthermore, 
they  rapidly  disappear  with  the  lapse  of  stimulation.  Still  less  is 
the  effect  of  repetition  to  be  disposed  of  as  a  case  of  "  fatigue."  a 
term  which  the  uncritical  lay  reader  might  readily  suggest.  Nothing 
like  fatigue  (used  in  the  sense  of  waste  products  and  lowered 
metabolism)  is  here  observed;  and  the  proposal  of  that  term  as  an 
hypothesis  would  be  a  loose  use  of  the  argument  from  analog}", 
which  explains  nothing.  If  genuine  fatigue  were  actually  induced 
by  rotation,  its  effects  would  scarcely  remain  unmodified  for  four 
or  five  days.  The  explanation  of  the  observed  decline  in  nystagmus 
remains,  therefore,  for  further  experimentation  made  under  more 
favorable  technical  conditions  than  the  department  has  been  able  to 
command.1 

The  present  experiments  have  demonstrated  (1)  that  organic  dis- 
turbances tend  to  disappear  under  rotation  day  after  day  and  (2) 
that  the  after-nystagmus  is  reduced  in  violence  and  in  duration  under 
repetition  (a)  within  a  single  experimental  series — a  total  rotation 
of  about  three  minutes — and  (&)  day  by  day.  In  10  turning  days, 
with  10  observations  made  each  day,  the  average  decline  for  six 
subjects  was  approximately  15  seconds,  or  more  than  half  the  original 
duration  finally.  The  experiments  have  illustrated  (3)  the  fact  that 

1  Unquestionable  evidence  now  available  (see  editorial  insert  immediately  following) 
disproves  the  statement  that  "  repetition  of  turning  certainly  leads  to  a  decrease  in 
after-nystagmus."  Of  the  six  individuals  used  by  the  psychologic  department  for  these 
experiments  not  one  was  examined  physically  beforehand ;  two  of  these  six  were  dis- 
covered subsequently  to  be  pathologic,  the  other  four  had  meantime  been  lost  sight  of. 
This  failure  to  establish  positively  the  normality  of  the  individual  subjects  before  pro- 
ceeding with  the  series  of  tests  is  most  unfortunate  as  it  makes  it  impossible  to  draw 
any  scientific  conclusions  from  the  data  obtained. 


MANUAL   OF    MEDICAL  RESEARCH    LABORATORY.  193 

casual  observation  of  nystagmus  involves  a  number  of  observational 
errors  which  may  be  eliminated  by  the  standardized  procedures  of 
the  psychological  laboratory. 

EDITORIAL    INSERT. 

The  foregoing  sets  forth  the  result  of  certain  ear  investigations 
which  were  undertaken  in  the  department  of  psychology.  Neither 
the  findings  in  the  individual  cases  herein  reported  nor  the  deductions 
drawn  from  the  series  are  in  accord  with  the  findings  and  deductions 
of  the  otologic  department. 

Several  thousand  reexaminations  of  fliers,  made  by  skilled  otolo- 
gists who  have  been  occupied  with  daily  turning  chair  examinations 
of  the  internal  ear  for  unbroken  periods  covering  12  to  18  months,  do 
not  indicate  reduction  in  the  duration  of  ii3rstagmus  following  rota- 
tion. A  carefully  analyzed  report  of  541  consecutive  cases  examined 
by  a  single  observer  on  three  of  the  southern  flying  fields  follows : 

One  hundred  and  fifty-six  men  examined.  Flying  period,  0  to  25  hours. 
Average  nystagmus — turning  to  right,  25T4SV,  turning  to  left,  25fVV  seconds. 

One  hundred  and  sixty-nine  men  examined.  Flying  period,  25i  to  50  hours. 
Average  nystagmus — turning  to  right.  2~>-^w;  turning  to  left,  25  r^  seconds. 

Fifty-nine  men  examined.  Flying  period,  50i  to  75  hours.  Average  nystag- 
mus— turning  to  right,  19 -SV;  turning  to  left,  18  ££  seconds. 

Thirty-seven  men  examined.  Flying  period,  75£  to  100  hours.  Average 
nystagmus — turning  to  right,  24|f ;  turning  to  left,  25iV  seconds. 

Twenty-one  men  examined.  Flying  period,  100|  to  150  hours.  Average 
nystagmus — turning  to  right,  25 If;  turning  to  left,  25 ^8T  seconds. 

Thirty-four  men  examined.  Flying  period,  150|  to  200  hours.  Average 
nystagmus — turning  to  right,  -tJ^;  turning  to  left,  25^  seconds. 

Thirty-two  men  examined.  Flying  period,  200i  to  250  hours.  Average 
nystagmus — turning  to  right,  23^;  turning  to  left,  23|f  seconds. 

Fourteen  men  examined.  Flying  period.  250*  to  300  hours.  Average  nystag- 
mus— turning  to  right,  23^;  turning  to  left.  25T\  seconds. 

Nineteen  men  examined.  Flying  period,  3004  to  1,000  hours.  Average  nys- 
tagmus— turning  to  right,  2(5T4S ;  turning  to  left,  25|£  seconds. 

The  average  nystagmus  of  accepted  applicants  among  75,000  ex- 
aminations showed  on  turning  to  the  right,  23  seconds,  and  on  turn- 
ing to  the  left,  23.1  seconds.  It  will  be  noted  that  the  average  nystag- 
mus of  the  above  series  is  somewhat  higher.  It  will  also  be  shown 
by  the  fact  that  without  dividing  these  cases  by  the  hours  of  flying, 
the  average  on  turning  to  the  right,  was  24.6  seconds,  and  turning  to 
the  left,  24.4  seconds. 

A  series  of  daily  observations  made  by  otologists  who  have  had 
years  of  daily  practice  in  the  application  of  turning  chair  tests  of 
the  internal  ear  was  conducted  in  the  laboratory  at  Mineola.  The 
subjects  of  this  series  of  tests  were  10  adult  individuals  carefully 
determined  by  previous  physical  examination  to  be  normal.  (No 
evidence  exists  as  to  the  normality  of  four  subjects  of  the  tests  con- 
ducted by  the  psychologic  department ;  the  other  two,  A  and  S,  were 
89119—18 13 


194 


MANUAL   OP   MEDICAL  RESEARCH   LABORATORY. 


found  upon  physical  examination  to  be  pathologic.  It  must  be  espe- 
cially emphasized  that  pathologic  conditions  of  the  internal  ear  not 
affecting  hearing  may  be  of  a  nature  very  difficult  to  detect  by  ordi- 
nary observations ;  for  example,  the  sequelae  of  mumps,  lues,  typhoid 
fever,  and  other  acute  infectious  diseases.)  Six  subjects  were  turned 
each  morning  ( 10  turns  to  the  right  in  20  seconds  and  10  turns  to  the 
left  in  20  seconds)  and  four  subjects  were  turned  in  the  same  manner 
both  morning  and  evening.  It  was  noted  as  the  subjects  became 
accustomed  to  the  vertigo  induced  by  turning  that  with  the  profi- 
ciency attained  in  executing  voluntary  motor  coordinations  manifest 
in  pointing  tests  and  fall  tests,  a  commensurate  proficiency  be- 
came apparent  in  voluntary  fixation  of  the  gaze  through  daily  prac- 
tice. This  acquisition  of  an  increased  fixation  control  of  the  volun- 
tary eye  movements  resulted  in  a  lessening  of  the  duration  of  the 
resulting  nystagmus  in  some  cases.  That  this  was  in  no  sense 
the  result  of  change  in  character  or  intensity  of  the  vestibular  stimu- 
lus was  proven  by  placing  before  each  subject's  eyes  a  pair  of  plus 
20  lenses  which  rendered  fixation  of  the  gaze  impossible.  Observa- 
tions of  the  resulting  nystagmus,  made  not  only  through  these  lenses 
but  behind  them,  confirmed  beyond  qeustion  the  finding  that  there 
was  no  reduction  in  the  duration  of  the  nystagmus  following  nine 
weeks  of  uninterrupted  tests. 

FREY,  j.  c. 


Date. 

A.M. 

P.M. 

Date. 

A.M. 

P.  M. 

Right. 

Left. 

Right. 

Left. 

Right. 

Left. 

Right. 

Left. 

Sept  26 

23 
20 
23 
21 
19 
20 
19 
20 
19 
20 
23 
17 
18 
21 
21 
20 
19 
22 
24 
19 
21 
21 
22 
23 

22 
22 

21 
24 
17 
19 
17 
18 
18 
21 
18 
20 
19 
19 
21 
19 
20 
18 
19 
21 
19 
19 
19 
19 
17 
19 

20 
28 

Oct.  26... 

20 
21 
19 
20 
25 
21 
19 
20 
22 
22 
24 
21 
21 
27 
21 
19 
21 
20 
21 
22 
19 
24 
23 
20 

20 
21 
18 
21 
19 
18 
20 
19 
19 
20 
21 
20 
18 
25 
19 
19 
20 
21 
20 
19 
19 
20 
20 
19 

27 

28  

22 
17 
19 
22 

17 

20 
16 
18 
1<) 
16 

28 

29  

30 

20 
19 
18 
21 
21 

18 
18 
18 
19 
19 

30  

Oot  1 

31  

2 

Nov.  1  

3 

3  

4 

4  

19 
19 

18 
18 

5 

5  

7 

21 
17 
21 
19 

18 
17 
20 
17 

6  

g 

7  

g 

8  

21 

26 
26 

22 
20 
20 

lj 

11  

12 

12  

14 

19 
22 
19 
20 
18 
20 
18 
20 
18 

19 
23 
19 
18 
16 
18 
21 
21 
17 

13  

15 

14  

16 

16  

17 

18  

18 

19  

21 

20  

25 

20 

22 

21  

23 

22  

21 

20 

24 

25  

25 

26  

SCHNEIDER,  T.  G. 


Sept  28 

25 

20 

Oct.   8... 

20 

16 

18 

16 

30 

26 

25 

23 

22 

9  

19 

20 

21 

20 

31 

26 

25 

10  

21 

25 

24 

16 

Oct   1 

29 

21 

12  ;. 

22 

19 

2 

28 

28 

19 

24 

14  

19 

17 

18 

19 

4 

19 

25 

18 

21 

15  

21 

22 

18 

21 

5 

18 

20 

16  

22 

25 

19 

15 

7... 

23 

26 

16 

17 

17... 

28 

26 

25 

21 

MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 
SCHNEIDER,  T.  G.— Continued. 


195 


Date. 

A.M. 

P.M. 

Date. 

A.M. 

P.M. 

Right. 

Left. 

Right. 

Left. 

Right. 

Left. 

Right. 

Left. 

Oct     18 

23 
19 
19 
17 
24 
20 
27 
27 
22 
26 
29 
21 
29 
31 
21 

18 

23 
24 
16 
18 
19 
17 
21 
24 
21 
28 
27 
21 
26 
27 
28 

19 

Nov.     7.  .  . 

26 
27 
25 

21 
22 
27 
22 
22 
24 
24 
27 
24 
26 
23 
25 
25 

iq 

8  

26 

24 

21 

18 
20 
24 

20 

19 
18 
18 
18 

9 

23 

12.   . 

26 
26 
28 
25 
30 
28 
24 
27 
25 
30 
25 
27 

24 

13  

27 
26 

28 
24 

25 

14  

26 

15     ... 

28 

24 
24 

23 
27 
17 
28 
27 
29 

23 

29 
29 
24 

16  

29 

18 

30 

19.   .   . 

25 
23 

ae 

21 
20 
21 

31 

20  

Nov      1 

21  

4 

26 
24 
30 

22.   . 

5 

25  

20 
24 

6 

26 

ENN1S,  L.  E. 


Sept.  26    .  .  .  . 

26 

26 

20 

19 

Oct.     19... 

18 

18 

30 

24 

28 

18 

20  

18 

20 

20 

20 

28 

30 

26 

22            .   . 

25 

26 

26 

27 

30     .... 

31 

25 

28 

25 

23     

20 

16 

19 

20 

Oct.      2  

24 

24 

22 

30 

24  

22 

20 

21 

20 

3 

27 

24 

31 

26 

25        .   . 

17 

18 

•  15 

20 

4  

23 

20 

26  

28 

25 

5 

22 

16 

28 

Ifi 

21 

25 

23 

7 

20 

23 

29     . 

23 

30 

25 

27 

10  

25 

21 

26 

19 

30  

26 

21 

23 

25 

11 

24 

22 

19 

19 

31 

20 

24 

24 

20 

12     .   .   .   . 

23 

21 

Nov.     3     . 

21 

22 

14  

24 

21 

19 

21 

4   

28 

24 

15 

20 

21 

21 

19 

5 

18 

24 

20 

23 

16  

20 

20 

19 

16 

8     . 

28 

28 

29 

23 

17  

24 

29 

23 

23 

9  

26 

28 

18 

22 

17 

19 

16 

LONG,  C.  M. 


Sept.  26  

26 

24 

26 

26 

Oct.  25  .. 

15 

'  16 

25 

24 

27 

20 

28  

19 

16 

18 

18 

28... 

24 

22 

29  

19 

19 

18 

20 

30  .... 

23 

27 

21 

22 

30 

21 

20 

20 

20 

Oct.   1  

25 

23 

31  

24 

23 

24 

23 

2  

26 

23 

24 

20 

Nov.  1  

18 

23 

17 

24 

3  

25 

25 

21 

20 

3  

23 

24 

4  

19 

16 

20 

16 

4  . 

27 

26 

17 

14 

19 

20 

5  

18 

20 

18 

18 

8. 

18 

18 

6 

21 

20 

20 

18 

9  

18 

18 

18 

18 

10  

16 

16 

18 

16 

12  

22 

2) 

20 

19' 

11  

17 

18 

17 

16 

13 

21 

20 

23 

20 

12  

20 

18 

14  . 

24 

21 

14  

18 

17 

17 

16 

16  

25 

25 

15  

19 

18 

18 

22 

21 

21 

22 

17  

20 

19 

19 

16 

19  . 

25 

23 

24 

22 

18  

20 

22 

19 

18 

20  

19 

24 

18 

21 

19  

22 

21 

21 

26 

24 

21  

21 

17 

19 

16 

22  . 

23 

20 

30 

19 

22  

21 

25 

18 

19 

23  

18 

18 

23  

16 

18 

17 

16 

25  

23 

20 

24  

14 

22 

19 

17 

26  . 

20 

18 

196  MANUAL   OP   MEDICAL  RESEARCH    LABORATORY. 

TRIMMER,  H.  M. 


Date. 

Right. 

Left. 

Date. 

Right. 

Lett. 

Sept    26  

24 

28 

Oct.    24 

21 

24 

20 

28 

25 

21 

23 

28 

26 

25 

28 

22 

23 

30  

25 

27 

29 

25 

27 

Oct.      1  

27 

22 

30  

25 

25 

2                       

22 

25 

31 

28 

26 

3  

21 

20 

Nov.     1 

19 

23 

4  

18 

21 

3.. 

20 

22 

5                     .... 

21 

21 

4 

27 

26 

7  

20 

23 

5 

24 

23 

9  

20 

22 

6  . 

25 

23 

10  .. 

24 

23 

7 

20 

19 

11  

18 

21 

8 

29 

28 

12  

24 

20 

9  . 

22 

24 

14 

18 

24 

11 

24 

30 

15  .                  .... 

20 

22 

12 

24 

24 

16  

19 

22 

13. 

25 

21 

17  

24 

27 

16..              ... 

26 

24 

18 

25 

21 

18 

26 

28 

19       

24 

24 

19 

22 

26 

21  

20 

18 

21   . 

24 

23 

22 

21 

22 

22 

22 

21 

23                         

22 

28 

26 

25 

21 

McCABE,  C.  J. 


Sept    28      .-         

27 
33 
27 
22 
20 
23 
20 
23 
24 
22 
24 
23 
23 
21 
22 
22 
24 
23 
19 
18 
17 
25 

27 
25 
27 
23 
19 
20 
21 
21 
24 
22 
23 
20 
22 
19 
24 
23 
19 
23 
24 
21 
19 
24 

Oct.    28 

22 
25 
23 
26 
26 
30 
27 
23 
21 
27 
25 
24 
27 
26 
24 
25 
26 
25 
21 
25 
24 

25 
28 
22 
29 
25 
30 
29 
21 
19 
26 
22 
21 
25 
28 
23 
22 
22 
24 
24 
23 
21 

Oot       1      

29  

2  

30  

3                       

Nov      1 

4                  

3 

5       

5                       

7  

6  

8 

7 

9  

8  

10                

9  . 

11        

11  

12  

12  

14  

13  

15                           

14 

16                

16.. 

17  

18  

18  

19  

21  ,  

21  

22                            

22 

23          

23  ..   . 

24  

26  

26  

BROWNING,  E.  L. 

Sept    26  

26 
22 
24 
27 
25 
27 
22 
22 
21 
23 
21 
22 
25 
16 
20 
23 
20 
24 
22 
16 

28 
26 
25 
23 
24 
24 
20 
21 
20 
19 
20 
23 
21 
20 
21 
21 
19 
19 
21 
19 

Oct.    25  

20 
30 
26 
18 
22 
22 
27 
27 
25 
30 
25 
20 
26 
25 
23 
21 
24 
30 
26 

91 
28 
24 
19 
23 
27 
26 
26 
22 
30 
27 
23 
28 
26 
24 
22 
25 
30 
27 

27 

26 

2S 

28 

30                            

29.   . 

Oct.      1     

30  

2  

31  

3 

Nov      5 

4                              

8 

5  

9  

7  

11  

8 

12 

9.   ... 

13 

10  

14...     .                               

11  

16  

12 

is                              

14 

19                                     

15  

20  

22  

21  

23     . 

22                                     

24 

MANUAL   OF    MEDICAL  RESEARCH    LABORATORY, 
HAYMAN,  G.  C. 


197 


Date. 

Right. 

Left. 

Date. 

Right. 

Left. 

Sept  28 

40 

37 

Oct.  30... 

28 

29 

Oct   2 

38 

36 

31  

30 

20 

3 

24 

30 

Nov.  1  

30 

28 

7 

31 

30 

3  

23 

27 

g 

33 

30 

4  

26 

28 

9 

31 

34 

5  

32 

33 

10 

32 

34 

6  

30 

26 

11 

30 

33 

7  

27 

21 

12 

30 

30 

9  

29 

26 

14 

32 

28 

11  

30 

28 

15 

30 

32 

12  

29 

26 

16 

23 

27 

13  

36 

30 

17 

31 

30 

14  

29 

27 

18 

26 

25 

16  

30 

27 

19 

05 

17  

30 

27 

21 

27 

25 

18... 

31 

30 

23 

33 

29 

20  

28 

28 

24 

23 

32 

21... 

34 

29 

25 

24 

23 

22  

30 

25 

26 

34 

27 

26  

30 

26 

29                ... 

34 

34 

BRAMLEY,  R.  H. 


Sept  28 

30 

33 

Oct.  23... 

20 

22 

Oct.   1 

29 

33 

25  

19 

23 

2 

40 

31 

26  

25 

31 

3 

25 

29 

28  

21 

23 

7 

29 

29 

29 

26 

28 

8 

24 

29 

30  

28 

26 

9 

25 

26 

31  

24 

28 

10 

29 

29 

Nov.  1      

25 

24 

11 

27 

28 

3  

25 

24 

12 

22 

24 

4  

27 

28 

15 

22 

21 

5    

25 

28 

16 

25 

24 

7  

26 

29 

17 

28 

26 

8 

26 

28 

18  

27 

32 

9  

35 

37 

19 

21 

22 

12  

30 

38 

21 

19 

21 

14         ... 

32 

30 

22  

22 

28 

JAFFA,  B.  B. 


Sept.  28  

2R 

34 

Nov.  1  ... 

26 

26 

Oct.   2  

28 

31 

*  3 

27 

27 

3  

34 

30 

4  

26 

25 

11 

31 

31 

5 

30 

29 

12   

28 

29 

6 

25 

27 

14  

22 

26 

7  

31 

30 

15  

26 

30 

9 

31 

28 

16  

30 

33 

11 

36 

28 

18  

27 

30 

12  

30 

28 

19  

25 

25 

13 

32 

34 

21  

25 

24 

14  . 

29 

30 

22  

30 

30 

16  

25 

27 

23  

20 

21 

18 

27 

26 

24  

23 

21 

19  

28 

27 

25  

20 

23 

20 

28 

26 

26  

24 

23 

21  . 

31 

32 

28  

24 

25 

22  

31 

29 

30  

28 

27 

26 

30 

26 

31  

22 

25 

It  is  of  supreme  importance  for  the  reader  to  note  the  cardinal 
difference  between  the  series  of  541  examinations  of  fliers  here  re- 
ported, in  whom  no  reduction  in  the  duration  of  nystagmus  was  en- 
countered, and  the  turning  chair  tests  conducted  upon  10  subjects  for 
9  consecutive  weeks.  The  flier  can  not  practice  the  fixation  of  gaze 
owing  to  the  variability  of  conditions  under  vHch  he  flies;  the  sub- 


198  MANUAL   OF    MEDICAL  RESEARCH   LABORATORY. 

jeet  in  the  turning  chair  must  fix  his  gaze  accurately  after  each  turn- 
ing, thereby  undergoing  a  very  intensive  practice  in  gaze  fixation. 

Jt  follows,  therefore,  that  when  a  marked  redutcion  in  duration  of 
nyxtagmu-s  is  encountered  it  must  be  regarded  as  indicating  a  definite 
departure  from  the  normal.  Examples  in  point  are  the  following 
three  cases: 

M,  flying  instructor,  reported  that  his  cadet  students  were  prone  to 
level  off  with  left  wing  down ;  officer  in  charge  of  flying  and  post  com- 
mander observed  that  M  always  leveled  off  with  the  right  wing 
down.  He  was  ordered  up  for  physical  examination,  which  revealed 
pathologic  condition  of  his  internal  ear,  evidenced  among  other  find- 
ings by  6  seconds'  duration  nystagmus  after  turning  right. 

W,  a  flier,  who  had  been  determined  by  a  physical  examination  to 
be  normal ;  after  completion  of  flying  training  in  England  had  sev- 
eral months'1  combat  service  on  the  western  front,  giving  daily  evi- 
dence of  satisfactory  flying  ability.  Officer  in  charge  of  flying  noticed 
gradually  increasing  loss  of  flying  ability ;  three  weeks'  rest  was  not 
followed  by  the  expected  improvement,  and  he  was  ordered  up  for  a 
reexamination.  His  nystagmus  record  on  entering  flying  training 
was  26  seconds  after  right  turn,  26  seconds  after  left  turn;  on  this 
reexamination  it  was  found  to  be  7  seconds  right  turn,  9  seconds  left 
turn.  Further  examination  revealed  luetic  internal  ear  disease;  the 
aviator  then  stated  he  had  acquired  syphilis  since  admission  into  the 
service. 

Lieut.  X  under  flying  instruction,  was  reported  by  instructor  as  a 
very  dangerous  pupil,  having  repeatedly  leveled  off  with  left  wing 
down ;  instructor  refused  to  take  further  risks.  Officer  in  charge  of 
flying  upon  looking  up  record  of  physical  examination  found  that 
through  clerical  error  this  man  had  been  reported  fit  for  flying  train- 
ing instead  of  unfit  for  flying  training  owing  to  subnormal  nystag- 
mus following  turning.  In  all  three  of  these  cases  the  diagnosis 
of  internal  ear  abnormality  was  made  by  the  flying  instructor  solely 
upon  the  evidence  furnished  by  the  flier's  performance  in  the  plane. 
Further  evidence  of  this  character  was  discovered  in  certain  of  the 
flying  fields  following  epidemics  of  mumps,  a  condition  affecting  the 
internal  ear  with  especial  frequency.  [End  of  editorial  insert.] 

2.  Orientation. — Methods  have  been  devised  for  determining  the 
promptness  and  the  accuracy  with  which  the  aviator  gets  his  bear- 
ings, finds  his  way,  and  remembers  his  course  in  the  air.  The  ability 
to  keep  directions  and  to  maintain  a  correct  orientation  on  the  ground 
or  in  flight  differs  widely  from  individual  to  individual,  and  since 
both  personal  safety  and  successful  execution  depend  upon  clear  and 
prompt  orientation,  the  test  of  a  pilot's  ability  in  this  regard  is  of 
great  importance.  Various  typical  means  of  orientation  distinguish 
one  flier  from  another.  The  main  "  types  "  discovered  and  described 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  199 

include  (1)  the  compass  type,  or  those  individuals  who  get  their  bear- 
ings by  the  cardinal  directions;  (2)  the  mapping  type,  individuals 
who  refer  places  and  directions  to  an  imaginary  map  upon  which 
north  is  always  before  and  east  at  the  right  of  the  observer;  (3)  the 
pointing  type,  which  depends  upon  kinsesthetic  factors  for  orienta- 
tion; (4)  the  pathfinding  type,  which  relies  upon  the  recognition  of 
landmarks;  (5)  the  fragmentary  type,  which  is  oriented  only  in 
certain  regions  and  under  certain  circumstances;  (6)  the  disoriented 
type,  which  includes  the  habitually  confused  and  muddled;  and 
(7)  the  lost  type  of  individual,  who  takes  little  or  no  account  of 
spatial  clues  to  position  and  direction  and  who  can  not  be  trusted 
to  explore  new  regions  or  to  search  out  a  new  objective.  Both  the 
accuracy  of  exploration  and  the  appropriate  method  of  instruction 
in  map  making  and  map  reading. and  in  reconnaissance  depend  upon 
the  flyer's  orientational  type. 

Apparatus  (figs.  20  and  21)  has  been  built  in  the  laboratory  for 
discovering  whether  the  pilot  or  the  observer  is  easily  lost  or  dis- 
oriented, whether  he  knows  and  keeps  his  compass  points,  and 
whether  he  is  capable  of  translating  verbal  orders  to  fly  to  a  named 
objective  into  a  plan  of  flight,  or  of  charting  a  terrain  from  his 
aerial  observations,  or  of  retracing  his  course  of  flight  by  the  observa- 
tion of  landmarks. 

The  test  of  the  methods  evolved  has  made  it  evident  that  it  is  pos- 
sible to  determine  within  a  few  minutes  the  "  type  "  of  the  aviator 
with  respect  to  orientation,  and  also  his  facility  in  getting  his  bear- 
ings and  in  maintaining  his  directions  under  the  exigencies  of  flight. 

3.  Association  reaction  times. — A  large  amount  of  work  has  been 
done  on  the  association  reaction  test  using  the  chronoscope  and  voice 
keys  (fig.  22).  In  this  test  a  word,  "stimulus  word"  spoken  by  the 
psychologist,  starts  the  hand  of  the  chronoscope  in  rotation,  and  a 
word,  "  response  word  "  spoken  by  the  reactor,  stops  the  hand.  The 
time  between  stimulus  and  reaction,  the  time  required  to  "think  of. 
the  reply  "  is  then  read  directly  on  the  dial  in  thousandths  of  a  second. 
Stimulus  words  of  a  definite  character  are  used  (e.  g.  nouns),  and  a 
response  word  of  definite  rotation  to  the  stimulation  word  (e.  g., 
verb  naming  action  which  could  be  exerted  by  whatever  is  desig- 
nated by  the  noun)  is  required.  In  this  way  a  rating  on  the  basis  of 
the  time  required  for  the  answer,  and  also  on  the  reliance  and  specific 
appropriations  of  the  answers  is  possible.  These  vary  according  to 
the  general  mental  ability  and  the  particular  condition  (fatigue,  etc.) 
of  the  reactor.  So  far,  the  work  has  been  largely  directed  to  the  de- 
velopment of  standard  lists  of  stimulus  words  (which  in  itself  re- 
quires a  large  amount  of  research)  and  the  perfecting  of  a  rating 
scheme, 


200  MANUAL   OF    MEDICAL   RESEARCH    LABORATORY. 

The  foregoing  enumeration  by  no  means  exhausts  the  immedi- 
ate possibilities  and  needs  of  investigation  of  the  points  of  general 
and  special  fitness  and  adaptability  noted  in  an  earlier  summary 
(Chap.  I).  Nor  does  it  include  all  the  work  on  these  topics  which 
is  under  way  in  the  psychological  laboratory.  It  indicates,  however, 
the  scope  of  the  work  in  the  direction  of  classificatory  tests,  and  to- 
gether with  the  preceding  statements  will  serve  as  a  guide  to  psycholo- 
gists in  the  various  fields  in  observing  fliers  and  flying  conditions  and 
collecting  information  useful  for  further  development  of  practical 
aid  to  the  service. 

VII.— DEPARTMENT  OF  NEUROLOGY  AND  PSYCHIATRY. 

The  Avork  of  this  department  touches  the  aviation  problems  at 
three  vital  points:  (1)  By  the  detection  in  the  aviator  of  symptoms 
of  nervous  and  mental  diseases;  (2)  by  the  recognition  of  latent 
trends  of  temperament  which,  if  not  recognized  in  time  and  treated 
rationally,  increase  the  liability  of  the  flier  either  to  become  ineffi- 
cient or  to  lose  morale  and  esprit  de  corps,  and  (3)  finally  by  supple- 
menting the  information  already  obtained  in  other  departments  in 
regard  to  the  aviator's  potential  flying  capacity  with  additional  data 
bearing  upon  his  temperament  and  personality.  This  knowledge  to 
be  used  in  the  selection  of  fliers  for  special  tasks. 

The  examiner  should  keep  constantly  before  his  own  mind  the 
fact  that  the  chief  purpose  of  these  personality  studies  is  to  determine 
the  fitness  of  an  aviator  to  withstand  the  nervous  strain  of  flying 
at  the  front.  For  this  reason,  although  clinical  methods  of  examina- 
tion are  used  in  taking  these  histories,  they  should  not  be  judged  by 
ordinary  clinical  standards — as  the  purpose  is  not  to  carry  the 
analysis  of  the  aviator's  personality  further  than  is  necessar}^  to 
estimate  his  potential  as  a  flier  under  war  conditions. 

The  chief  sources  of  information  for  data  upon  which  judgment 
of  the  personality  is  based  are  (1)  the  Aviator  under  examination, 
(2)  other  Departments  in  the  laboratory,  (3)  the  Flight  Commander, 
and  (4)  the  Flight  Surgeon.  A  spirit  of  sympathetic  cooperation  is 
necessary  in  gathering  this  data  and  neurologists  and  psychiatrists 
should  remember  they  are  attempting  merely  to  supply  some  of  the 
links  in  a  relatively  long  chain  of  evidence. 

In  estimating  the  nervous  capacity  to  withstand  strain  the  ex- 
aminer should  give  particular  attention  to  the  following  points: 

(1)  What  were  the  chief  reasons  influencing  the  aviator  in  choos- 
ing this  branch  of  the  service?  Did  the  love  of  adventure,  desire  for 
independent  action,  or  interest  in  machinery,  or  a  combination  of  all 
these  elements  enter  into  the  decision?  Does  he  feel  that  he  is 
making  good  and  is  he  satisfied  with  his  original  decision?  The 


MANUAL   OF    MEDICAL  RESEARCH    LABORATORY.  201 

statements  of  experienced  aviators  show  how  much  success  in  fly- 
ing depends  upon  making  that  particular  decision  clean  cut  and 
then  accepting  it  as  final.  Indecision,  a  sense  of  inadequacy,  or  idle 
regret  at  having  chosen  work  for  which  he  is  not  fitted  tempera- 
mentally may  lead  to  a  chain  of  symptoms  culminating  in  a  psychosis 
or  psychoncnrosis. 

(2)  Impressions  of  the  aviator's  readiness  or  disinclination  to  face 
difficult  situations  fairly  and  squarely  should  be  recorded.    Evidence 
of  a  tendency  to  dodge  critical  events  in  life,  a  habit  which  if  not 
corrected  may  become  the  starting  point  for  morbid  fears  and  ob- 
sessions, should  be  noted.    An  experienced  and  daring  aviator  may 
lose  nerve  suddenly  as  the  result  of  not  having  definitely  settled  some 
relatively  trivial  event  of  a  personal  nature.     States  of  irresolution 
and  doubt  as  well  as  compulsions  antagonistic  to  efficiency  often 
develop  out  of  buried  mental  complexes. 

(3)  The  question  should  be  asked  whether  the  members  of  the 
immediate  family  approve  or  disapprove  of  his  flying,  making  it 
easy  or  difficult  for  the  aviator  to  devote  his  entire  attention  to  his 
work. 

(-4)  Notice  should  also  be  taken  of  the  occurrence  of  nervous  or 
mental  disorders  in  the  family  history. 

Associated  with  the  effort  to  present  brief  records  containing  only 
the  essential  facts  in  each  case,  there  should  also  be  a  clear  apprecia- 
tion of  the  number  and  variety  of  factors  which  may  affect  the  be- 
havior of  the  aviator.  Each  analysis  should  be  based  on  the  consid- 
eration of  the  active  forces  influencing  behavior  in  critical  situations. 
The  restriction  of  the  investigation  merely  to  taking  a  cross  section  of 
life  at  any  single  level  in  the  life  curve  is  not  sufficient.  Remotely 
antecedent  events  in  life,  such  as  attacks  of  disease,  accidents,  circum- 
stances giving  rise  to  bad  habits,  or  poor  educational  opportunities, 
may  have  a  direct  practical  bearing  on  the  performances  of  the 
aviator  in  a  plane. 

The  following  cases  are  cited  to  illustrate  the  advantages  of  a  very 
brief  summary  of  the  life  history. 

CASE   1.— Personality   rating,    "A."     No   indication   that   he   will   require   any 
special  attention  nor  be  predisposed  to  collapse  tinder  strain. 

,  1st  lieut,  A.  S.  S.  0. 


Aviation  history :  No  "  repeats "  in  ground  school.  Licensed  pilot.  80  hrs. 
flying  to  date.  No  accidents. 

Personal  history :  No  serious  illness  nor  accidents.  Public-school  education ; 
not  college  graduate.  Has  worked  hard  for  living  and  enjoyed  it.  No 
grouches.  Normally  optimistic.  Advised  by  his  captain  in  Infantry  to 
transfer  to  aviation.  Glad  he  did  so;  enjoys  flying;  feels  he  is  m;iking  good. 

Physical  examination :  Height,  5  ft.  6  in. ;  weight,  132 ;  age,  23.  Nothing 
abnormal. 


202  MANUAL   OF   MEDICAL   EESEABCH   LABOBATOBY. 

Tests  (low  tension)  :  Very  good,  "A." 

Personality  study :  Stocky,  muscular  type ;  look  steady,  countenance  cheerful, 
but  not  overemotional.  Activity,  good ;  discipline,  good ;  willing  to  take 
chances  if  necessary.  Stability  under  strain  probably  excellent.  Good 
judgment. 

CASE  2. — Personality  rating,  "  B."    Safe  if  watched  for  development  of  nervous 
symptoms. 


-,  flying  cadet,  A.  S.  S.  C. 


Aviation  history:  Ground  school;  difficulty  with  wireless  (has  poor  musical 
sense).  8  hrs.  flying  to  date.  No  accidents. 

Personal  history :  Nothing  of  importance  in  family  history  except  "  mother 
worries  greatly  about  me  "  and  writes  to  him  on  this  subject.  College  gradu- 
ate (4  yrs.),  Harvard,  A.  B. ;  worked  his  way  through  college  and  has  also 
worked  in  munition  factory.  No  pronounced  reasons  given  for  choosing 
aviation.  Unmarried. 

Physical  examination :  Height,  5  ft.  6  in. ;  weight,  140  Ibs. ;  age,  24.  Nothing 
abnormal  noted. 

Tests  (low  tension:  — . 

Personality  study :  Short,  well  knit ;  regular  features,  mobile,  expression  tense 
but  under  control ;  anxious  to  understand  and  please.  Manner  tense  and 
high  strung.  Keen  sense  of  responsibility.  Ambitious  and  keenly  interested 
in  his  work,  but  inclined  to  take  even  trivial  events  too  much  to  heart.  Will 
do  his  duty  but  needs  careful  watching  when  he  gets  to  the  front.  Should 
be  watched  for  signs  of  staleness  or  beginning  nervousness,  loss  of  sleep,  etc. 

CASE  3. — Personality  rating,  "  D."    Probably  not  safe  if  flying  at  the  front. 


Aviation  history :  No  trouble  in  ground  school ;  work  in  ground  school  described 
as  easy. 

Personal  history.  Bright  at  bookwork ;  high-strung  always ;  exceedingly  popular 
with  friends.  Has  had  most  of  children's  diseases;  no  complications  nor 
accidents.  Great  interest  in  athletics.  Public  schools  and  college.  Entered 
service  from  junior  class.  Unmarried. 

Physical  examination:  Very  active  knee  jerks.  Pupils  show  secondary  expan- 
sion, after  dilatation.  Height,  6  ft. ;  weight,  155 ;  age,  24. 

Tests  (low- tension) : 

Personality  study:  Decidedly  self-conscious;  slightly  aggressive  manner;  very 
high-strung  and  overemotional.  Lacks  normal  subjective  feeling  of  fatigue 
after  hard  exercise.  Talks  a  great  deal  and  rapidly.  Gives  the  impression 
of  working  under  great  pressure.  Is  decidedly  nervous  and  lacks  voluntary 
control  of  expenditure  of  energy.  Reserve  store  of  energy  limited.  Would 
probably  not  stand  strain  of  active  service  at  the  front. 

Accompanying  each  history  a  personality  summary  is  made  on  a 
separate  slip  in  order  to  present  the  essentials  in  as  brief  form  as 
possible  for  the  use  of  the  Commanding  Officer.  If  more  detailed  in- 
formation is  required,  this  can  be  obtained  by  reference  to  the  labora- 
tory records. 


MANUAL   OF    MEDICAL  RESEARCH   LABORATORY.  203 

PERSONALITY  SUMMARY.     No.  — . 

HAZELHURST  FIELD,   MINEOLA,   N.    Y. 


Aviation  history 

Personal  history 

Physical  examination- 
Tests  (low-tension)  — 
Personality  study 


Rating : 

Personality- 


Tests   (low- tension). 


A  summary  of  the  cases  already  examined  in  this  department  with 
an  explanation  of  ratings  follows. 

The  object  of  the  personality  study  is  to  determine:  (1)  Whether 
neuroses  or  psychoses  actually  exist  or  (2)  whether  there  are  any 
indications  in  the  temperament  or  personality  of  the  aviator  sug- 
gesting that  tendencies  now  latent  under  the  stress  of  war  conditions 
may  give  rise  to  symptoms  of  nervous  shock,  diminishing  efficiency 
and  impairing  morale. 

Personality : 

"A". — Safe.     Nervous  and  mentally  stable. 

"  B  ". — Safe,  with  limitations. 

"  C  ". — Questionable ;   no  definite  conclusion  reached. 

"  D  ". — Needs  special  attention. 

"  K  ". — Unsafe. 

Not  rated. 
Tests  (low-tension)  : 

"A". — No  restrictions. 

"B".— Should  not  fly  above  15,000  feet, 

"C".— Should  not  fly  above  8,000  feet. 

"  D  ".—Should  not  fly  at  all. 
Personality  studies: 

Rating    "A" 46 

Rating    "  B  " 29 

Rating  "  C  " 16 

Rating  "  D  "___. ' 1 

Rating  "  E  "___ 1 1 

Not  rated 18 

Total-  -   111 


204       •  MANUAL   OF    MEDICAL   RESEARCH    LABORATORY. 

Low-tension  tests : 

Rating  "A" 27 

Rating  "  B  " 26 

Rating  "  C  " 14 

Rating  "  D  " 6 

Not  rated  _.  38 


Total 111 

Agreement,  personality  rating,  and  tests 36 

Nonagreement  personality  rating  and  tests 29 

One  or  both  ratings  absent 46 


Total 111 

The  discrepancies  noted  between  personality  ratings  and  test  rat- 
ings are  no  evidences  of  marked  differences.  The  low-tension  tests 
are  made  with  the  object  of  determining  the  aviator's  capacity  to 
meet  changes  incident  to  variations  in  barometric  pressure,  whereas 
the  aim  of  the  personality  studies  is  to  determine,  if  possible,  the 
resisting  capacity  for  nervous  and  mental  shocks. 

In  collecting  this  material  for  records  great  care  should  be  taken 
not  to  suggest  imaginery  troubles  to  the  person  being  examined. 
Babinski  and  Froment  (Hysterie-Pithia-tisme  et  troubles  nerveux 
d'ordre  reflexi  Collection  Horizon.  Precis  de  Medicine  et  de  Chir- 
urgie  de  Uuerre,  Masson  &  Cie.,1918)  have  emphasized  the  increased 
danger  of  "  suggestion  "  as  an  etiological  factor  of  nervous  diseases 
in  the  life  of  the  soldier.  A  great  deal  therefore  depends  upon  the 
tact  and  good  judgment  of  the  examiner. 

A  very  important  function  of  the  wrork  of  the  department  is  to 
make  clear  the  value  of  'good  mental  hygiene  in  increasing  efficiency 
in  assisting  in  the  maintenance  of  discipline  on  rational  grounds  in 
strengthening  morale  and  contributing  to  the  esprit  de  corps  essen- 
tial for  a  complete  and  final  military  victory. 

Informal  conferences  on  the  subject  of  the  mental  hygiene  of  the 
aviator  should  be  of  practical  value.  The  demoralizing  influences 
of  intemperance,  using  the  word  in  a  broad  physiologic  sense,  the 
paralyzing  effects  of  worry  over  unsolved  personal  problems,  of  the 
failure  to  get  square  \vith  life,  of  anxiety  about  anticipated  events, 
and  the  shock  caused  by  suddenly  awakening  to  the  realization  of 
the  fact  that  the  lure  of  wish-directed  thoughts  make  an  individual 
incapable  either  of  judging  or  facing  reality. 

The  casualty  list  in  the  Aviation  Service  can  be  greatly  reduced 
by  insisting  upon  the  necessity  of  cultivating  a  frank,  open  attitude 
of  mind  in  the  treatment  of  the  various  problems  which  are  forced 
upon  the  attention  of  the  flier.  Staleness,  loss  of  confidence,  various 
phobias,  and  increasing  emotional  instability  are  insidious  enemies. 


Legend 


..Diast.  B    P. 


in  cl-cil.  per  min.       ••••— •    Syst.  B.  P 


D.R.,    A?B:    20-6/12 

Mitral    «teno«is   anrt    Insufficiency.      High 
pulse   and   blood-presfiuro.     labored   res- 
piration.       Fall'ng   diaetolic   pressure 
at  end  indicating;  circulatory  exhaustion. 
"ClaaB  D" 


No.  217.— D.  R. 


CADET. 


Age  20  years,  6  month?. 


There  was  a  roughening  of  the  first  heart  sound  heard  before  the  test.  No  demonstrable 
enlargement,  second  sounds  equal.  During  the  test  a  definite  systolic  murmur  developed 
and  the  pulmonic  second  was  accentuated.  There  is  no  doubt  of  the  diagnosis  of 
mitral  insufficiently  well  compensated. 

The  chart  is  typical  of  most  cases  of  valvular  lesions.  The  pulse  is  high  throughout 
the  test.  The  systolic  pressure  is  high  and  uniform.  Diastolic  pressure  begins  to  fall 
between  9  and  10  per  cent,  but  is  in  control  at  all  times.  Respiration  shows  rather  a 
marked  response.  Efficiency  is  well  preserved,  the  psychological  note  being  A.  This 
is  accomplished  at  the  expense  of  marked  overwork  of  the  heart.  Although  this  is  well 
borne  at  the  present  time,  the  presumption  is  that  the  subject  would  soon  show  the 
effects  of  wear,  and  permanent  damage  to  the  heart  might  easily  result.  Class  D. 


205 


205 


MANUAL   OF    MEDICAL  RESEARCH    LABORATORY.  205 

Aviators  should  be  familiar  with  the  methods  of  preventing  the 
formation  of  some  of  the  mental  influences  disorganizing  both  to 
temperament  and  character.  The  difficult  task  of  keeping  their  nerve 
should  not  be  made  unnecessarily  difficult  by  the  failure  to  appreciate 
and  apply  a  few  of  the  principles  of  good  mental  hygiene. 

HELPING  THE  AVIATOR  TO  KEEP  HIS   NERVE. 

No  one  doubts  the  desirability  of  maintaining  within  the  aeroplane 
and  its  motor  the  conditions  essential  for  maximum  flight  efficiency. 
There  are  only  a  few  people,  however,  who  recognize  the  necessity 
for  detecting  and  remedying  the  disturbances  of  the  delicate  nervous 
and  mental  adjustments  of  the  aviator  controlling  the  machine. 
In  the  air  service  of  the  allied  armies  the  lists  of  casualties  due 
to  preventable  and  unknown  causes  are  very  much  longer  than  the 
ones  containing  the  names  of  aviators  killed  in  battle.  Many  of  these 
fatalities  are  due  to  the  failure  of  those  directing  the  activities  of 
the  aviator  to  take  cognizance  of  his  imperfect  emotional  and  mental 
adjustments. 

A  long  list  of  accidents,  however,  is  not  the  only  deplorable  effect 
of  the  failure  to  assist  the  aviator  to  keep  his  nerve  and  his  head 
in  critical  situations.  The  human  machine  loses  efficiency  much  more 
rapidly  through  neglect  to  provide  the  conditions  essential  for  good 
headwork  than  the  motor  does  when  it  is  not  well  oiled  or  its  parts 
are  not  kept  thoroughly  adjusted.  If  even  half  as  much  care  as  is 
now  given  the  machinery  of  the  planes  was  devoted  to  finding  out 
whether  the  emotional  and  mental  balance  of  the  aviator  was  equal 
to  the  strain  to  which  it  is  subjected  it  would  be  possible  to  develop 
the  fighting  efficiency  of  the  air  forces  to  a  much  higher  degree  than 
exists  at  present. 

The  aviator  in  action  has  to  be  heart  and  soul  in  his  work.  Neither 
his  attention  nor  interests  can  be  divided,  even  for  an  instant. 

Very  brief  periods  of  distractibility,  uncertainty,  or  slight  anxiety ' 
at  critical  moments  may  end  quickly  in  a  catastrophe.  In  many  occu- 
pations, even  in  military  life,  these  momentary  lapses  may  not  end 
disastrously,  but  the  chances  of  their  doing  so  while  the  aviator  is 
in  the  air  are  a  thousand  times  greater.  The  emotional  and  mental 
balance  of  the  aviator  should  be  so  very  delicately  adjusted  that  it 
responds  instantly  and  accurately  whenever  the  unexpected  strain 
of  the  critical  situation  is  thrown  upon  it.  The  aviator  has  practically 
no  opportunity  to  correct  his  mistakes.  A  wrong  impulse,  uncon- 
trolled emotion,  or  thought  not  related  to  the  situation  may  be  the 
cause  of  disaster.  This  principle  is  equally  true  whether  the  aviator 
is  high  in  the  air  or  approaching  the  ground. 

Disasters  resulting  from  hesitation  or  indecision  in  the  compara- 
tively difficult  though  necessary  procedure  of  landing  may  be  and 


206  MANUAL   OP   MEDICAL  RESEARCH   LABORATORY. 

undoubtedly  are  often  due  to  a  certain  mental  or  nervous  instability 
not  generally  demonstrated  by  the  ordinary  methods  of  observation 
or  medical  supervision.  These  disturbances  of  the  mental  balance 
are  demonstrable  and  capable  of  being  ameliorated  by  neurologic 
or  psychiatric  methods.  The  dangers  of  indecision  or  divided  atten- 
tion when  in  combat  or  even  when  in  the  usual  "  formations,"  now 
the  rule  in  aerial  warfare,  may  be  easily  visualized  and  can  hardly 
be  overestimated.  In  the  illustration  (the  jackals,  p.  19)  the  im- 
portance of  maintaining  position  in  "formation"  is  emphasized. 
This  maneuver  requires  great  mental  alertness  and  good  judgment. 
The  danger  of  possible  collision  with  other  fliers  in  the  "  formation 51 
can  only  be  avoided  by  unswerving  attention  •  and  coordinated  and 
instantaneous  action. 

What  are  some  of  the  causes  which  lead  to  momentary  but  often 
fatal  inefficiency?  Anxiety,  worry,  straining  to  repress  harassing 
memories  of  personal  trouble,  a  sudden  and  temporary  but  over- 
whelming sense  of  inadequacy  in  facing  a  crisis  very  often  interfere 
with  the  transmission  of  the  coordinated  motor  impulses  from  the 
brain.  An  aviator  having  an  excellent  record,  though  trying  hard 
but  unsuccessfully  to  repress  any  recollection  of  worry  over  personal 
problems,  may  lose  his  nerve  and  refuse  to  fly,  or,  on  the  other  hand, 
he  may  attempt  to  fly  while  the  mental  conflict  is  still  acute  and  end 
his  career  with  a  fatal  crash.  An  aviator  struggling  hard  to  repress 
and  forget  these  nerve-wrecking,  disorganizing  ideas  and  anxieties 
is  a  menace  to  himself  and  the  whole  organization  until  by  frankly 
talking  the  matter  over  with  some  sensible  person  he  "  gets  it  off  his 
chest."  The  first  step  in  the  restoration  of  efficiency  and  nerve  con- 
sists in  facing  squarely  the  real  cause  of  his  anxiety  instead  of  try- 
ing to  evade  it. 

Even  the  aviator  who  is  mentally  and  physically  fit,  may  be  thrown 
into  a  condition  of  mental  irritability  and  anxiety,  which  he  is  not 
able  to  control,  upon  the  receipt  of  depressing,  unreasonably  solicit- 
ous, or  even  threatening,  letters  from  home.  Frequently  states  of 
apprehensiveness  and  anxiety  affect  the  aviator  to  a  far  greater  ex- 
tent than  he  realizes  or  is  willing  to  admit  even  to  himself. 

There  are  different  types  of  personality  which,  on  account  of  their 
special  intellectual  qualities,  are  now  generally  recognized  as  possess- 
ing the  temperamental  qualities  antagonistic  to  success  in  aviation. 
Among  the  types  which  require  special  supervision  are  men  with 
decided  variations  in  mood  or  emotional  tone.  We  all  know  men,  in 
our  own  circle  of  acquaintances,  in  whom  such  variations  are  marked ; 
men  who  may  be  classed  at  times  as  extreme  optimists,  at  other  times 
swinging  over  to  the  opposite  or  pessimistic  pole  of  emotional  ex- 
perience. Within  certain  limits  and  under  intelligent  medical  super- 


MANUAL   OF   MEDICAL  RESEABCH   LABORATORY.  207 

vision,  this  group  of  men  may,  and  probably  do,  furnish  some  of  the 
most  versatile  and  daring  of  the  aviators.  On  the  other  hand,  we 
are  confronted  by  the  fact  that  these  same  men  if  permitted  to  swing 
to  the  extremes  of  the  emotional  arc  will  certainly  become  casuals 
or  casualties.  They  may  develop  on  the  one  hand  into  the  cases  of 
unbalanced  manic-depressive  make-up,  latent  hysterical  trends,  and 
many  cases  showing  symptoms  of  the  anxiety  neuroses. 

The  question  of  mental  hygiene,  as  related  to  the  aviator,  should  be 
given  a  great  deal  of  attention.  The  reduction  of  the  efficiency  of 
the  soldier  through  any  form  of  intemperance  is  now  generally 
recognized;  and  similar  effects,  but  to  a  far  greater  extent,  are  ob- 
served in  the  case  of  the  aviator.  The  type  of  man  making  the  suc- 
cessful aviator  is  often  high  strung  and  impulsive  and  requires 
plenty  of  outlet  for  his  energies.  These  outlets  can  be  easily  pro- 
vided in  ways  entirely  satisfactory  to  him  and  conducive  to  his 
efficiency  without  injuring  the  brain  and  the  nervous  system  as  does 
dissipation.  He,  himself,  does  not  seek  dissipation;  but,  having  an 
enormous  amount  of  unexpended  energy,  he  seeks  some  channel — any 
channel-*-for  its  discharge.  Adequate  provision  should,  therefore,  be 
made  for  recreation  and  suitable  forms  of  mental  relaxation  if 
the  dangers  of  dissipation  are  to  be  avoided. 

The  supervision  of  the  aviator  outlined  above  has  been  definitely 
included  as  a  part  of  the  duties  of  the  Flight  Surgeons.  It  is  planned 
that  the  Flight  Surgeons  shall  receive  instruction  and  advice  rela- 
tive to  the  methods  of  observation  and  examination  of  the  fliers  at 
the  Medical  Research  Laboratory  or  other  centers  of  instruction. 
That  specialists  in  psychiatry  can  not  be  trained  in  the  short  time 
available  is  clearly  recognized.  On  the  other  hand  it  is  possible  for 
the  Flight  Surgeon  to  obtain  a  certain  point  of  view  toward  his  prob- 
lem and  for  him  to  become  definitely  informed  concerning  the  types 
of  personality  referred  to  in  the  preceding  paragraphs.  The  prob- 
lem of  the  training  of  the  Flight  Surgeon  therefore  resolves  itself 
into  one  of  method  of  observation  and  examination. 

The  neuro-psychiatric  examination  is  brief;  sufficiently  brief  to 
get  it  all  on  one  page.  First  is  given  an  account  of  the  aviator's  en- 
trance into  the  Air  Service,  of  his  aviation  school  work,  and  the 
chief  causes  which  led  to  his  selection  of  this  branch  of  the  service. 
It  is  important  to  know  whether  the  choice  of  this  branch  of  the 
service  was  made  voluntarily  and  enthusiastically;  whether  he 
drifted  into  it  and  is  more  or  less  indifferent  or  even  unhappy  in  it. 
Then  follows  an  account  of  his  Army  life  preceding  his  entrance 
into  aviation.  Finally  in  this  part  of  the  investigation  a  note  is 
made  of  the  number  of  hours  of  flying,  and  also  whether  there  have 
been  any  accidents.  A  brief  personal  history  follows  the  family 
history,  with  reference  to  the  diseases  or  injuries  he  has  had.  Com- 


208  MANUAL   OF    MEDICAL   RESEARCH   LABORATORY.         \ 

paratively  slight  disorders  may  be  the  cause  of  great  harm.  Ton- 
sillitis is  an  example.  Attention  is  paid  to  his  school  and  college 
record,  with  mention  of  his  athletic  record.  These  data  tell  us  some- 
thing as  to  the  sports  in  which  he  was  proficient  and  give  us  a  fair 
idea  of  his  skill  as  well  as  of  his  temperament  qualities. 

The  attitude  of  the  family,  especially  the  mother  and  wife,  are 
noted,  whether  it  is  one  of  sympathetic  approval  or  disapproval,  and 
this  has  an  important  influence  upon  his  capacity  to  keep  his  nerve. 
We  also  try  to  ascertain  whether  he  has  definite  cause  for  worry. 
Sometimes  there  are  periods  when  the  aviator  prefers  not  to  fly,  but, 
on  the  other  hand,  he  is  usually  very  keen  for  his  work,  and  it  is  only 
when  something  has  gone  wrong  that  his  enthusiasm  wanes;  some- 
times disturbing  influences  emanate  from  home;  sometimes  he  feels 
'•  fed  up  "  and  wants  a  holiday.  Many  influences,  both  internal  and 
external,  may,  if  powerful  at  the  critical  moment,  throw  him  off  his 
mental  balance.  The  aviator's  balance  and  alertness  must  be  main- 
tained at  the  highest  efficiency  while  he  is  flying.  At  intervals,  when 
for  any  reason  his  full  potential  efficiency  is  not  maintained,  he 
should  not  fly  nor  until  he  is  again  at  his  best,  both  physically  and 
mentally.  Great  tact  should  be  exercised  in  gathering  the  data.  A 
great  deal  of  information  of  importance,  often  of  a  personal  nature, 
would  not  be  divulged  unless  the  examination  brought  it  easily  to 
light  and  demonstrated  to  the  aviator  its  importance. 

Third,  a  brief  physical  examination  is  made.  The  reactions  of  the 
pupils  and  extrensic  muscles  and  the  knee  jerks  for  evidence  of 
hypertension  or  hyperexcitability  are  recorded.  Sometimes  we  get 
signs  of  fatigue  in  these  reactions;  sometimes  signs  of  emotional 
hyperactivity.  The  presence  of  tremor  in  the  extension  of  the  hands 
and  in  the  handwriting,  as  well  as  in  the  process  of  drawing  hori- 
zontal and  vertical  lines  freehand,  is  also  mentioned. 

Tests  for  dermagraphia  before  and  after  flying  or  before  and  after 
the  rebreathing  tests  are  made.  Definite  conclusions  relative  to  these 
tests  have  not  been  reached  as  yet,  but  our  attention  has  been  drawn 
to  certain  groups  of  symptoms.  We  have  looked  upon  a  tendency 
of  the  line  to  spread  or  blotch  as  rather  connected  with  other  signs 
of  fatigue  and  disability.  This  reaction  is  frequently  accompanied, 
though  not  always,  by  nervous,  very  lively  knee  jerks  and  an  emo- 
tional instability.  A  secondary  pupillary  reaction  is  sometimes  asso- 
ciated with  this  group  of  symptoms. 

Occasionally  after  the  rebreathing  or  after  flying  a  blushing  is 
observed  a  finger's  width  on  either  side  of  the  line.  This  seems  to 
be  of  more  or  less  importance,  taken  in  conjunction  with  the  other 
symptoms  mentioned.  But  whether  this  deduction  can  be  borne  out 
by  further  observation  remains  to  be  seen. 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  209 

Lastly,  we  record  our  impression  of  the  aviator's  personality.  We 
observe  whether  he  is  open  and  frank  in  his  talk  or  reserved  and 
inhibited.  We  note  his  emotional  state,  trying  to  determine  whether 
he  is  in  a  contented  frame  of  mind  or  whether  he  is  disgruntled  and 
does  not  want  to  say  so  or  whether  he  is  "  fed  up."  It  is  important  to 
determine  as  closely  as  possible  what  the  reason  is  that  he  is  on  edge 
or  out  of  sorts.  With  this  object  in  view,  a  record  is  kept  of  even 
slight  fluctuations  of  moods. 

Frequently  we  run  across  men  in  a  state  of  mental  anxiety  mild 
or  acute.  A  little  tactful  questioning  will  usually  bring  out  the 
causes.  These  causes  may  be  simple  and  easily  removable,  or  they 
may  be  complicated  and  persistent.  The  points  bearing  on  the  case 
must  be  talked  over  frankly  and  conscientiously.  Late  hours,  loss  of 
sleep,  too  many  cigarettes  will  easily  lower  the  resistance.  Worry 
and  anxiety  of  any  sort  in  the  otherwise  perfectly  healthy  and  well- 
set-up  man  will  surely  reduce  his  efficiency.  Even  steady  attendance 
upon  his  work  to  the  point  where  he  is  "  fed  up  "  will,  if  persisted 
in,  produce  signs  of  mental  and  nervous  strain  and  soon  render  him 
a  danger  in  the  air. 

In  a  short  study  of  the  personality  we  determine  whether  the  flyer 
is  aggressive  or  on  the  defensive,  whether  he  has  initiative  and  cour- 
age or  is  reckless  and'irresponsible,  whether  he  makes  quick  or  slow 
decisions,  whether  he  is  a  high-pressure  engine  under  control,  and 
whether  his  judgments  are  likely  to  be  good.  His  reactions  during 
the  examinations  are  important.  He  may  give  active  cooperation, 
and  this  is  a  good  sign,  or  he  may  leave  us  with  the  impression  that 
the  result  of  the  examination  wa?  unsatisfactory;  even  this  indefi- 
nite finding  may  later  have  an  important  bearing  on  the  personality 
study  and  should  be  recorded.  These  and  other  items  help  us  to  gain 
a  fairly  definite  impression  of  our  man. 

Nervous  states  nearer  the  border  line  of  the  psychoses  are  occasion- 
ally observed.  The  importance  of  detecting  these  cases  and  weeding 
them  out  is  apparent,  and  we  should  appreciate  how  easily  they  may 
escape  recognition.  Many  cases  which  under  conditions  of  ordinary 
life  do  not  develop  into  psychoses  in  all  probability  will  take  this 
unfavorable  turn  under  the  strain  and  stress  of  war. 

Our  whole  object  is  to  determine  any  undesirable  psychomotor  or 
other  reaction  that  indicates  that  the  man  is  wholly  or  in  part  unfit 
for  flying.  We  accomplish  this  in  as  brief,  direct,  and  practical  a 
way  as  possible.  After  the  examination  the  man  is  classified  accord- 
ing to  estimated  efficiency,  judged  from  the  neurologic  and  psychia- 
tric point  of  view.  The  classifications  are  A,  B,  C,  D,  E. 

Explanation  of  personality  rating: 

A=Safe,  nervous,  and  mentally  stable. 
B=Safe,  with  limitations. 
89119—18 14 


210  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

C= Questionable;  no  definite  conclusion  reached. 
D= Needs  special  attention. 
Ei=Unsafe. 

In  order  to  illustrate  some  of  the  different  types  and  give  an  indi- 
cation of  the  methods  of  making  personality  studies  the  following 
cases  are  cited : 

PERSONALITY  RKCOKD. — No.  194. 

WHITE  FIELD,  N.  H.,  June  S,  1918. 
H.  R.  S.,  1st  It,  RSSR.,  pilot. 

Aviation  history :  Officers'  Training  Camp  June  to  July  30,  1917 ;  ground  school 
to  Aug.  5,  1917 ;  to  E.  Field  to  Dec.  20,  1917 ;  to  J.  Field  March  31,  1918 ;  com- 
missioned Feb.  6,  1918;  to  S.  Field  to  date.  260  hrs.  flying  to  date.  No 
crashes. 

Personal  history :  Measles  and  scarlet  fever,  good  recovery.  Appendicitis  1915, 
operation  successful.  Father  dead,  age  53,  chronic  nephritis ;  mother  living 
and  well ;  1  sister  living  and  well.  Mother  does  not  approve  of  aviation,  be- 
lieving it  too  hazardous  for  her  son.  Mother's  concern  has  "  modified  his 
actions ;  more  careful."  This  is  doubtful.  Not  particularly  athletic.  Educa- 
tion, high  school  and  college. 

Physical  examination:  Ht,  69;  \vt,  136;  age,  24.  Knee  jerks  active.  Fine 
tremor  in  fingers,  constant ;  pupils  react  normally  to  light  and  accommodation. 
No  secondary  dilatation. 

Personality  study :  Quiet,  some  reserve ;  has  to  be  interested  in  flying  to  follow 
it  or  make  it  a  success ;  deeply  interested  in  flying ;  anxious  to  get  across ; 
"  getting  tired  of  wasting  further  time  in  training."  Was  disappointed  three 
weeks  in  not  being  transferred  to  Columbus  and  in  not  getting  leave  of  ab- 
sence. Wants  aerial  gunnery  ;  has  had  100  hrs.  formation ;  getting  disgusted ; 
feels  physically  tired  from  continued  flights  and  frequent  trips  to  New  York. 
(Impatient.)  Emotion  easily  excited  toward  end  of  examination. 

Rating :  Personality,  "  E."     Tests,  low-tension. 

PERSONALITY  RECORD. — No.  207. 

Station  -     — ,  Date  -     — . 
B.,  R.,  2d  lieut.,  —  squadron,  pilot. 

Aviation  history :  Enlisted  aviation  section  Sept.,  1917 ;  graduated  from  ground 
school  Jan.  20,  1918;  Kelly  Field,  San  Antonio,  Tex.,  to  June  10,  1918; 
to  R.  F.  to  date.  150  hrs.  flying  to  date.  2  accidents.  2  crashes,  both 
from  low  altitude  in  high  wind,  2  days  following  first  solo  flight.  Not 
injured. 

Personal  history:  Father  and  mother  alive  and  well.  Glad  to  have  him  in 
aviation.  Athletic  training,  track,  basketball,  horseback,  mountain  climbing. 
6  to  10  cigarettes  daily,  not  inhaled.  Education,  high  school,  university  2 
yrs.  Civil  occupation,  civil  engineering.  Unmarried.  Res.,  Ogden,  Tex. 

Physical  examination:  Ht.,  66;  wt,  125  (usual  weight);  age,  24.  Pupils 
normal  to  light  and  accommodation.  Tonsils  operated  in  childhood ;  visible 
stumps,  enlarged  cervical  glands.  Knee  jerks  lively.  No  tremor  of  hands. 

Personality  study:  Wears  an  expression  of  slight  apprehension.  Looks  tired, 
a  little  pale,  and  not  fit.  Says  he  turns  in  at  night  at  12  or  2  usually. 
Nearly  fainted  yesterday  while  being  examined  (at  medical  department). 


MANUAL   OF    MEDICAL   RESEARCH    LABORATORY.  211 

He  seems  direct  and  frank,  but  I  can  not  feel  sure  of  this.  Gives  the 
impression  of  being  mentally  and  physically  tired.  Should  be  seen  again 
and  certainly  not  to  fly  at  present.  He  realizes  he  is  not  in  best  of  condition. 
Can  not  say  positively  there  is  any  psychic  evidence  of  his  lack  of  condition. 
May  be  due  to  tonsils. 
Rating:  Personality,  "E"  (temporarily  on  account  of  tonsils  and  fainting). 

PEBSONALITY  RECORD. — No.  193. 

BLACK  FIELD,  Date . 

J.,  H.  Q.,  1st  It.,  ASSRC.,  pilot. 

Aviation  history :  Ground  school  July  1st,  1917,  to  Oct.  1,  1917 ;  transf.  to  Black 
Field  to  May  30,  1918.  315  hrs.  flying  to  date.  No  crashes. 

Personal  history :  Typhoid  at  13  yrs.  Fractured  right  humerus  near  shoulder 
joint,  10  years  ago.  Athletic  training,  foot  and  base  ball,  swimming,  tennis; 
always  in  training.  Education,  4  yrs.  high  school,  3  yrs.  college.  Unmarried. 
Res.,  Philadelphia,  Pa. 

Physical  examination :  Ht.  70 ;  wt.,  154 ;  pulse  64,  high  tension ;  pupils,  equal 
active,  slight  secondary  dilatation ;  knee  jerks ;  active,  easily  exhausted. 

Personality  study :  Has  been  flying  constantly  since  last  year ;  has  felt  feeling 
of  staleness ;  "  loss  of  pep  "  for  1  month.  No  worries  or  fears,  merely  the 
wearing  of  the  steady  grind,  no  variety ;  at  present  only  formation  work. 
Quick,  accurate  responses.  Wants  change;  rest  for  a  week  or  two.  Should 
be  watched  during  convalescence  period.  Optimistic  as  to  future.  Increased 
motor  activity ;  sweating  localized ;  face  flushes  easily.  Has  dreamed  of 
flights  only  recently ;  of  being  in  tail  spin. 

Rating :  Pensonality,  "  E." 

PERSONALITY  RECORD. — No.  204. 


Field,  . 

P.  J.,  1st  lieut,  pilot. 

Aviation  history :  May,  1917,  Tech  School,  X  Field— to  date.     70  hrs.  flying  to 

date.    No  crashes. 
Personal  history :  Measles,  pneumonia,  and  recurring  tonsillitis  until  this  year. 

Broken  leg  2  yrs.   ago.     Father  living  and  well,   1  sister  living  and  well. 

Family  firmly  opposed  to  flying.     Wife  greatly  depressed  over  aviation.     2 

small  children.    Married.    Res.,  New  York,  N.  Y. 
Physical  examination :  Ht.,  68 ;  wt.,  165 ;   age,  25.     Knee  jerks ;  very  active. 

Pupils  react  normally  to  light  and  accommodation.     Slight  secondary  dilata- 
tion after  primary  dilatation,  after  primary  contraction. 
Personality  study :  An  excellent  type ;  open  frank,  genuine  forceful,  courageous. 

Has  personal  worries  and  has  good  cause  for  them. 
Rating :  Personality  :  "  E." 

PERSONALITY  RECORD. — No.  189. 

E.  FIELD,  June  29,  1918. 
S.  E.  J.,  2nd  lieut,  pilot. 

Aviation  history :  Ground  school  July  17-Jan.  18,  1918.   O.  Field,  Feb.  6,  '18-May 
30,  '18.    M.  Field,  to  date.    310  hrs.  flying  to  date.    No  accidents. 


212  MANUAL  OP   MEDICAL  RESEAECH   LABORATORY. 

Personal  history:  Measles  and  malaria  during  childhood;  t>phoid  at  15,  pneu- 
monia 16.  Athletic  training,  football,  basket  ball,  and  track.  Education, 
high  school,  2  yrs.  college.  In  Army  since  1915.  Xo  leave..  Tobacco,  15 
cigarettes  daily.  Alcohol,  moderate.  Family,  father  and  mother  living  and 
well ;  3  brothers  living  and  well.  No  opposition.  Unmarried.  Res.,  Rock 
Hill,  Ark. 

Physical  examination :  Ht,  71 ;  wt,  174 ;  age,  23.  C^vn't  relax  so  it  is  difficult 
to  obtain  knee  jerks  unless  attention  is  diverted  Pupils  active.  Marked 
secondary  dilatation. 

Peronality  study  :  Feels  stale  and  shows  some  emotional  instability.  Says  he 
has  not  had  an  accident,  but  knows  one  is  coming.  Probably  does  not  take 
very  good  care  of  himself.  Is  unsafe  for  flying  on  account  of  present  condi- 
tion. Should  have  vacation. 

Rating :  Personality :  "  D." 

VIII.— THE  REBREATHING  MACHINE. 

The  rebreathing  machine  in  its  simplest  form  consists  of  a  bag 
filled  with  air,  connected  by  a  tube  to  one  side  of  an  absorbing  can 
containing  caustic  soda  (see  fig.  1).  A  tube  leads  from  the  other 
side  of  the  can  to  a  mouthpiece.  A  clip  having  been  placed  on  the 
subject's  nose  and  the  mouthpiece  in  his  mouth,  he  breathes  into  and 
out  of  the  bag,  the  air  passing  through  the  caustic  soda,  which  re- 
moves from  it  all  of  the  exhaled  carbon  dioxide.  Inasmuch  as  a  part 
of  the  oxygen  contained  in  each  breath  is  abs/orbed  by  the  body  and 
the  carbon  dioxide  is  removed  by  the  caustic  soda,  the  volume  of  air 
in  the  bag  gradually  decreases  and  the  percentage  of  oxygen  in  the 
mixture  grows  progressively  less.  Starting  with  60  liters  of  air  in 
the  bag,  the  average  subject  will  reduce  the  oxygen  to  7  per  cent  in 
about  30  minutes. 

SIMPLE  FORM  OF  REBREATHING  APPARATUS. 

The  rebreathing  machines  in  use  in  the  laboratories  of  the  Medical 
Research  Board  embody  the  same  principle  as  the  simple  apparatus 
shown  above,  but  they  are  built  of  metal  and  are  designed  particu- 


iece. . 


SIMPLE  FORM  OF  REBREATHINQ  APPARATUS. 

larly  for  the  routine  testing  work  of  the  board.  There  are  at  present 
'Jiree  forms  of  the  machine  in  use,  called  respectively  type  A 
(serial  Nos.  2-13,  inclusive),  type  B  (serial  Nos.  14-22,  inclusive), 


THE   REBREATHER. 


212 


213 


MANUAL  OF   MEDICAL   EESEABCH    LABORATORY.  213 

and  type  C  (serial  Nos.  23-37,  inclusive),  but  they  differ  only  in 
details  and  a  description  of  one  will  serve  for  all  (see  fig.  2).  The 
base  of  the  machine  is  a  steel  tank  (T)  of  60  or  80  liters  capacity, 
according  to  the  type.  Type  A  has  80-liter,  and  types  B  and  C 
60-liter  tanks.  Air  is  inspired  from  the  tank  through  the  pipe  at  the 
left,  and  is  expired  back  into  the  tank  through  the  pipe  and  ab- 
sorbing cartridge  (A)  at  the  right.  The  valves  (VV)  keep  the 
air  stream  flowing  always  in  the  proper  direction.  In  order  to 
maintain  the  contained  air  at  approximately  atmospheric  pressure 
and  to  allow  for  changes  in  volume,  a  wet  spirometer  (S),  carefully 
counterbalanced,  is  mounted  on  the  tank  and  communicates  freely 
with  its  interior  through  the  vertical  pipe  (P).  A  stylus  attached  to 
the  counterweight  records  the  movements  of  the  spirometer  upon  the 
smoked  drum  of  the  kymograph  (K).  Water  is  admitted  to  the  tank 
through  valve  (E)  to  replace  the  volume  of  the  used  oxygen  and  also 
to  flush  out  the  tank  after  an  experiment.  The  water  is  drained  away 
to  the  sewer  by  means  of  valve  (F).  Valve  (C)  affords  a  free  open- 
ing to  the  atmosphere  for  flushing  the  tank  of  the  rebreathed  air. 
Valve  (D)  should  invariably  be  closed  while  flushing  the  tank,  other- 
wise water  will  enter  the  absorption  cylinder  (A)  and  ruin  the  car- 
tridge. The  cartridge  is  a  cylindrical  paper  tube  filled  with  solid 
caustic  soda,  cast  in  thin  shells  so  as  to  expose  a  large  surface  to  the 
action  of  the  gas.  It  is  prepared  for  use  in  the  machine  by  punching 
the  ends  full  of  quarter-inch  holes  with  a  pencil.  The  brass  ring  is 
then  inserted  in  the  lower  end  of  the  cartridge,  the  rubber  ring  fitted 
over  the  end,  and  the  whole  inserted  into  the  absorption  cylinder. 
Cartridges  should  never  be  used  without  both  rubber  ring  and  brass 
ring  in  proper  position.  Valve  parts  may  be  removed  from  the  air 
valves  (VV)  by  means  of  the  brass  spanner  wrench,  which,  together 
with  two  new  valve  parts,  is  furnished  with  each  machine.  Counter- 
weight slide  rods  should  be  frequently  greased  with  vaseline  and  the 
pulleys  oiled.  In  setting  up  a  machine  care  should  be  taken  to  level 
it  properly,  so  that  the  inner  can  of  the  spirometer  hangs  freely  in 
the  outer  can  and  does  not  rub  against  the  side. 

IX.— THE    LOW-PRESSURE    CHAMBER. 

The  low-pressure  chamber  at  the  Mineola  laboratory  is  a  cylin- 
drical steel  tank,  8  feet  in  diameter  and  10  feet  high,  standing  on 
end.  It  is  entered  through  a  full-sized  doorway  in  the  side,  and 
forms  a  commodious  and  comfortable  room  in  which  five  or  six  in- 
vestigators may  conduct  physiological,  psychological,  and  ophthal- 
mological  tests  under  conditions  of  reduced  atmospheric  pressure. 

The  reduction  of  pressure  is  brought  about  by  means  of  a  motor- 
driven  vacuum  pump  of  10  horsepower,  capable  of  rarefying  the 
atmosphere  within  the  chamber  to  a  barometric  pressure  of  14Q 


214  MANUAL  OF   MEDICAL  BESEARCH   LABOBATOBY. 


M 


U     Q 


JL 


LJ 


215 


MANUAL  OF   MEDICAL   RESEARCH   LABORATORY.  215 

millimeters  of  mercury  (equivalent  to  35,000  feet  above  sea  level) 
in  live  minutes.  This  is  more  than  sufficient  for  any  tests  upon 
human  beings. 

The  pump  withdraws  air  from  the  tank  through  a  3-inch  pipe  at 
the  top;  at  the  same  time  fresh  air  is  admitted  at  the  bottom,  the 
amount  being  regulated  by  means  of  a  valve.  The  admission  of 
air  in  this  manner  serves  the  double  purpose  of  ventilating  the  cham- 
ber and  of  determining  the  rate  at  which  the  pressure  is  reduced. 
That  is,  if  the  valve  is  wide  open,  pressure  remains  normal;  if  the 
valve  is  closed,  the  pressure  drops  rapidly.  Thus  by  manipulating 
one  valve  any  rate  of  pressure  rise  or  fall  may  be  secured. 

The  inside  of  the  chamber  is  finished  in  a  flat,  neutral  tint  and 
lighted  by  tungsten  "  daylight "  lamps.  Several  windows  of  thick 
glass  allow  experiments  to  be  watched  from  without. 

An  oxygen  supply  is  piped  through  the  wall  into  the  chamber  to 
a  distributing  board,  with  an  individual  tube  and  mouthpiece  for 
each  observer.  A  check  valve  in  the  pump  line  prevents  a  material 
drop  of  pressure  within  the  tank  if,  for  any  reason,  the  pump  is 
stopped. 

For  ease  and  efficiency  of  operation  the  control  has  been  cen- 
tralized. Directly  before  the  operator  is  a  small  window  and  a 
telephone,  enabling  him  to  observe  and  communicate  with  those  in- 
side. At  the  left  of  the  window  is  the  mercury  manometer  indicat- 
ing the  barometric  pressure  within  the  tank,  expressed  in  milli- 
meters of  mercury  and  in  feet  above  sea  level.  At  the  operator's 
left  hand  are  the  valves  regulating  the  oxygen  supply;  the  valves 
at  his  right  hand  control  the  flc«v  of  air,  and  below  them  is  the 
switch  for  the  motor.  The  operator  need  not  leave  his  post  from 
beginning  to  end  of  an  experiment. 

Figure  12  is  a  view  of  the  chamber. 

X.— THE  CLASSIFICATION  EXAMINATION. 

The  test  for  classification  of  aviators  is  an  outgrowth  of  the  re- 
search work  on  the  physiological  effects  of  low  atmospheric  pressure. 
It  was  found  that  there  were  wide  variations  in  the  resistance  to  such 
effects,  and  the  task  was  undertaken  of  determining  Avhich  indi- 
viduals were  most  suitable  for  the  branches  of  work  which  involve 
flying  to  the  higher  altitudes. 

The  method  of  rating  adopted  corresponds  well  with  the  military 
needs  of  the  service.  In  the  first  place  are  the  fighters,  the  pursuit 
pilots,  who  commonly  fly  about  15,000  feet,  often  above  20,000  feet. 
In  the  second,  the  bombers,  who  fly  comparatively  high  but  rarely 
above  15,000  feet.  Third,  the  observation  planes  keep  mostly  in  the 
lower  levels,  rarely  going  above  8,000  or  10,000  feet.  The  results  of 


216  MANUAL   OF    MEDICAL   RESEARCH   LABORATORY. 

the  low-oxygen  test  are  expressed  in  ratings  A,  B,  and  C,  correspond- 
ing to  the  above  requirements.  Class  D  includes  men  who  for  one 
reason  or  another  ought  not  to  fly  at  all;  such  cases  are  occasionally 
found,  though  the  purpose  of  the  test  is  classification  of  flying  per- 
sonnel rather  than  elimination  of  any.  After  several  hundred  tests 
have  been  made  it  was  found  that  the  number  of  men  passed  in  class 
A  (about  50  per  cent)  was  much  greater  than  the  need  of  the  service 
for  pursuit  pilots.  Siisce  choice  had  to  be  made  among  these  men 
anyway,  it  was  felt  that  a  still  higher  rating  was  desirable  which 
should  include  the  particularly  hardy  specimens  who  ought  by  all 
means  to  be  chosen  first.  For  this  reason  a  rating  of  A  A  is  given 
to  about  10  per  cent  of  men  examined. 

The  examinations  are  being  made  at  the  central  laboratory  at 
Mineola  and  at  a  number  of  the  flying  schools  in  this  country.  It  is 
hoped  later  to  send  examining  units  to  every  flying  field  here  and 
abroad,  and  also  to  make  the  examinations  at  an  earlier  period  in  the 
career  of  the  flier  .by  installing  examining  units  at  ground  schools  or 
other  concentration  points  for  candidates. 

The  examining  unit  consists  of  four  officers  and  six  enlisted  men. 
The  officers  are  a  physiologist  wrho  has  general  charge  of  the  conduct 
of  the  test  and  sees  that  the  technical  details  are  carried  out ;  a 
clinician  who  passes  on  the  general  physical  fitness  of  the  subject 
both  before  and  during  the  test,  especially  on  the  reaction  of  the 
heart  and  circulation;  a  psychologist  who  determines  the  effects  on 
general  efficiency  as  expressed  by  the  apparatus  work;  and  an 
ophthalmologist  who  makes  a  careful  preliminary  examina.tion  of  the 
eyes  and  determines  any  effects  oi^low  oxygen  upon  the  vision.  The 
enlisted  men  manage  the  rebreathing  machine,  make  air  analyses, 
record  pulse  and  blood  pressure  during  the  test,  and  do  the  clerical 
work  on  the  reports. 

The  routine  test  is  carried  out  as  follows:  A  careful  history  is 
recorded  and  a  general  physical  examination  made,  special  attention 
being  given  to  the  circulatory  apparatus.  The  reaction  of  pulse  and 
blood  pressure  is  measured  when  reclining  and  standing,  after  stand- 
ard exercise  (stepping  up  five  times  upon  a  chair) ,  and  two  minutes 
after  exercise.  It  is  hoped  that  these  simple  tests  will  be  found  use- 
ful when  repeated  later  in  the  career  of  the  flier  to  determine  whether 
he  has  remained  in  good  condition.  It  may  be  stated  that  a  normal 
behavior  in  these  reactions  has  been  found  to  be  a  very  fair  index  of 
the  subject's  ability  to  pass  the  low-oxygen  test.  A  careful  examina- 
tion is  now  made  of  the  eyes. 

The  next  step  is  the  rebreathing  test  itself.  The  evidence  is  suffi- 
cient that  this  test  is  a  perfectly  reliable  index  of  tolerance  to  low 
atmospheric  pressure,  and  the  low-pressure  chamber  has  been  used 


MANUAL   OF    MEDICAL  RESEARCH    LABORATORY.  217 

not  as  a  routine  method  of  examination  but  only  as  a  means  of  check- 
ing up  the  results  of  the  other  test  and  for  scientific  purposes. 

The  rebreathing  machine  is  so  adjusted  that  the  average  run  will 
be  between  25  and  30  minutes.  During  the  run  the  subject  does  the 
psychological  work  as  described  elsewhere  and  is  carefully  observed 
by  the  psychologist  to  determine  the  earliest  effects  on  attention  and 
motor  coordination,  as  well  as  the  time  of  appearance  of  more  marked 
effects  and  of  total  breakdown. 

Every  three  minutes  the  capacity  of  the  external  and  internal 
ocular  muscles  is  retested  during  the  run  (near  point  of  convergence 
and  near  point  of  accommodation).  During  the  whole  test  the  pulse 
and  blood  pressure,  systolic  and  diastolic,  are  measured  every  one  or 
two  minutes.  The  clinician  keeps  close  watch  of  these  figures  and 
makes  frequent  examinations  of  the  heart.  The  respiration  is  re- 
corded during  the  test  on  a  kymograph. 

The  test  ends  when  the  psychologist  has  determined  that  the  sub- 
ject has  reached  the  point  of  complete  inefficiency,  or  when  the  clin- 
ician finds  that  the  condition  of  the  circulation  makes  prolongation 
of  the  test  undesirable.  The  latter  contingency  usually  means  either 
that  the  heart  is  abnormal  or  that  fainting  is  about  to  occur  unless 
the  test  is  stopped.  At  the  close  of  the  run  the  air  remaining  in  the 
apparatus  is  analyzed  to  determine  the  oxygen  percentage  reached, 
which  can  be  translated  roughly  into  terms  of  altitude.  A  few  sub- 
jects have  exhausted  the  oxygen  to  6  per  cent  or  a  little  lower;  7  per 
cent  is  a  frequent  figure,  while  poor  subjects  either  become  inefficient 
or  faint  at  considerably  higher  percentages. 

The  results  of  the  test  are  summarized  in  a  plot  of  which  the  ab- 
scissa line  represents  minutes  of  time,  and  the  ordinates  are  per  cent 
of  oxygen,  and  figures  representing  pulse,  blood  pressure,  volume  of 
respiration,  millimeters  of  near  point  of  convergence,  etc.  The  ap- 
pearance of  different  degrees  of  inefficiency  by  the  psychological 
tests  is  indicated  by  symbols  placed  at  the  proper  time  on  the  ab- 
scissa line.  It  is  assumed  (with  reasonable  correctness)  that  a 
straight  line  connecting  the  oxygen  per  cent  at  beginning  and  end  will 
represent  the  per  cent  at  all  intervening  times.  The  basis  of  judg- 
ment on  the  success  of  the  subject  is  the  oxygen  percentage  at  which 
various  phenomena  occur,  and  this  is  reckoned  from  the  height  of  the 
oxygen  line  at  the  time  in  question. 

The  decision  as  to  rating  the  subject  is  made  by  consensus  of  opin- 
ion on  the  basis  of  the  ratings  made  by  each  separate  department  and 
is  ordinarily  the  lowest  rating  assigned  by  any  one  of  them.  No  man 
is  passed  in  class  A  who  has  any  considerable  disqualification  from 
any  point  of  view.  For  example,  a  deficiency  in  vision  whether  ordi- 
narily present  or  only  developing  as  the  result  of  the  test  would  dis- 


218  MANUAL   OF    MEDICAL   RESEARCH    LABORATORY. 

qualify  for  combat  work  no  matter  how  well  the  candidate  performs 
otherwise. 

Aside  from  ocular  deficiencies  or  general  physical  conditions  of  a 
distinctly  abnormal  nature,  the  rating  of  a  subject  depends  on  the 
answer  to  two  questions.  How  well  does  he  adapt  himself  to  the 
unusual  environment,  i.  e.,  how  well  does  he  preserve  his  efficiency  at 
altitudes  (as  expressed  by  the  psychological  tests)  and,  second,  at  the 
expense  of  how  much  strain  on  his  circulatory  system  does  he  do  it? 
Many  subjects  will  compensate  admirably,  preserving  their  efficiency 
to  a  very  high  altitude,  but  only  by  means  of  a  very  high  blood 
pressure,  high  pulse,  or  violent  vasomotor  reactions  such  as  would 
lead  us  to  expect  that  this  man  wrould  wear  out  quickly  in  service  or, 
perhaps,  actually  have  a  circulatory  collapse  in  the  air  and  faint. 

As  to  the  first  question,  that  of  general  condition  and  the  proper 
functioning  of  the  compensatory  apparatus,  our  most  delicate  cri- 
terion is  the  performance  on  this  psychological  test.  If  a  man  is 
able  to  keep  his  brain  clear,  he  is  certainly  compensating  against  low- 
oxygen  effects,  for  the  brain  is  not  only  the  most  important  tissue  to 
protect,  but  it  is  also  the  most  sensitive  to  defective  nutrition.  After 
much  experimentation  with  different  systems  of  rating  a  fairly  em- 
pirical method  of  computation  has  been  adopted  (fully  described 
elsewhere)  which  takes  into  account  the  percentage  of  oxygen  at 
which  various  effects  appear  and  the  duration  of  the  test,  since  longer 
exposure  to  moderate  oxygen  deficiency  may  produce  more  profound 
effects  than  a  short  exposure  to  a  high  degree.  The  rating  is  based 
both  on  the  early  slight  signs  of  abnormal  effect  and  on  the  more 
pronounced  manifestations  up  to  complete  inefficiency.  One  man  may 
be  moderately  inefficient  from  8,000  feet  up,  but  only  break  com- 
pletely at  25,000  feet.  Another  may  remain  perfectly  clear  until 
20,000  feet  and  then  suffer  a  complete  loss ;  probably  the  second  man 
would  be  a  more  useful  flier  than  the  first. 

The  second  question,  that  of  the  amount  of  circulatory  strain 
involved  in  preserving  compensation,  is  answered  largely  by  the 
behavior  of  pulse  and  blood  pressure  and  by  the  sound  of  the  heart 
during  the  test. 

A  fuller  discussion  will  be  found  elsewhere  of  the  method  of  rating 
based  on  circulatory  effect.  A  subject  who  has  a  definitely  diseased 
heart,  no  matter  how  well  compensated,  is  put  in  class  D,  and  it  is 
recommended  that  he  be  kept  at  ground  work.  No  man  is  passed 
in  class  A  whose  blood  pressure  is  so  high  that  the  heart  will  be 
continually  undergoing  severe  strain.  Signs  of  circulatory  exhaus- 
tion or  fainting  are  causes  for  rating  in  class  B  or  C. 

It  should  be  stated  that  some  of  these  circulatory  reactions  are 
signs  not  of  constitutional  inferiority  but  of  temporary  lack  of  con- 
dition. They  none  the  less  give  a  clear  index  of  how  the  man  may 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 


219 


be  expected  to  behave  in  the  air,  and  such  a  temporary  rating  should 
be  followed  until  a  better  general  condition  can  be  demonstrated.  It 
is  hoped  that  it  will  be  possible  to  apply  the  test  at  rather  frequent 
intervals  to  the  aviators  in  service  and  thus  determine  whether  they 
are  remaining  in  good  condition  or  becoming  "  stale."  For  this  reason 
it  has  been  arranged  that  the  report  of  the  examination  is  to  accom- 
pany the  aviator  wherever  he  goes  and  be  accessible  to  the  Flight 
Commander  and  the  Flight  Surgeon. 

An  analysis  has  been  made  of  the  results  of  374  routine  examina- 
tions. The  results  are  given  in  the  tables  below. 

The  first  table  shows  the  percentages  of  the  various  ratings  among 
various  classes  of  subjects  examined.  Pilots  and  cadets  show  almost 
identical  figures  for  the  higher  ratings,  but  more  absolute  disquali- 
fications were  recommended  among  the  latter.  Nonfliers  make  a 
considerably  poorer  showing. 

TABLE  No.  1. — Analysis  of  374  examinations. 


A 

A 

1 

L 

I 

) 

( 

1 

I 

) 

Num- 
ber. 

Per 
cent. 

Num- 
ber. 

Per 

cent. 

Num- 
ber. 

Per 

cent. 

Num- 
ber. 

Per 
cent. 

Num- 
ber. 

Per 

cent. 

Total. 

Pilots           

15 

9.4 

52 

32.7 

58 

36.5 

32 

20.1 

2 

1.3 

159 

Cadets        

16 

9.7 

54 

32.7 

58 

35.1 

27 

16.4 

10 

6.1 

165 

Total  fliers  
Observers       

31 
1 

9.5 
4.3 

106 
5 

32.7 
21.7 

116 
6 

35.9 
26.1 

59 
10 

18.2 
43.5 

12 
1 

3.7 
4.3 

324 
23 

Others     

1 

3.7 

7 

25.9 

7 

25.9 

7 

25.9 

5 

18.5 

27 

Total 

33 

8.8 

118 

31.7 

129 

34.6 

76 

20.3 

18 

4  8 

374 

The  average  age  of  the  various  classes  is  interesting, 
tabulated  for  193  cases  passed  above  D. 


This  was 


TABLE  No.  2. 


Number. 

Age. 

Class  A  A  

22 

Yrs.  Mas. 
23           9 

Class  A  

61 

25           1 

Class  B    

69 

91 

Class  C  

41 

24           7 

Among  109  cases  of  fliers  rated  class  B  the  reason  for  not  giving  A 
was  as  follows: 


Number. 

Per  cent. 

Circulatory  exhaustion  

37 

33  9 

Psychic  deterioration  

36 

33  0 

Both  of  above  

27 

24  8 

High  blood-pressure  

9 

8  3 

Total  

71 

100  0 

220  MANUAL   OF    MEDICAL  RESEARCH   LABORATORY. 

Among  65  cases  of  fliers  rated  C  the  reason  therefor  was: 


Number. 

Per  cent. 

Circulatory  exhaustion  

31 

47  7 

Psvchie  deterioration  

23 

35  4 

Both  of  above  

3 

4.6 

High  blood-pressure      

5 

7  7 

Defective  vision  

3 

4.6 

65 

100.0 

Of  18  men  rated  in  class  D  the  causes  were : 

Valvular  heart  disease 9 

Ventricular   extra  systoles 3 

Deficiency  of  vision  or  ocular  muscles 3 

Color  blindness _ 1 

Vertigo  of  unknown  cause 1 

Neurotic  constitution,  poor  vasomotor  tone 1 

Total 18 

XL— DIRECTIONS  FOR  THE   CLASSIFICATION   EXAMINATION. 
ROUTINE  FOR  EXAMINATIONS. 

1.  Each  unit  will  consist  of  four  officers  and  six  enlisted  men,  viz: 

1.  Physiologist. 

2.  Clinician. 

3.  Ophthalmologist. 

4.  Psychologist. 

Enlisted  men,  A,  B,  C,  D,  E.  and  F. 

2.  The  ranking  officer  of  each  unit  will  exercise  military  command 
and  will  coordinate  and  expedite  the  work  of  the  unit.     He  will  not. 
however,  usurp  the  right  of  other  officers  to  decide  matters,  especially 
such  as  involve  rating,  which  lie  in  their  own  departments.     Tech- 
'nicai  or  scientific  matters  or  such  as  involve  general  policy  will  be 
referred    to   the    Mineola    Laboratory    through   the    chiefs    of   the 
respective  departments. 

3.  The  routine  test  for  aviators  will  consist  of  (a)  preliminary  test 
by  clinician  and  physiologist  including  history,  (5)  preliminary  test 
by   ophthalmologist,    (<?)    test  on  the  rebreathing   apparatus   dur- 
ing which  the   subject's  performance  and   condition  are   observed 
by  clinician,  ophthalmologist,  and  psychologist.    Technical  details  of 
the  test  are  the  responsibility  of  the  physiologist  who  supervises  the 
work  of  the  enlisted  men  on  the  machine  and  in  taking  pulse  and 
blood  pressure.    He  will  not  examine  the  subject  during  the  test. 

1.  The  test  will  normally  be  continued  until  the  subject  has  arrived 
at  a  point  where  he  clearly  shows  low  oxygen  effects  or  his  efficiency 
as  determined  by  the  psychologist,  and  when  this  point  is  reached, 
the  experiment  will  be  terminated.  In  case,  however,  his  general 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  221 

condition  demands  it,  the  subject  should  be  removed  before  this  time. 
The  necessity  for  interrupting  the  test  before  its  natural  termination 
is  to  be  decided  by  the  clinician  though  all  others  present  should 
call  his  attention  to  unfavorable  indications.  This  applies  especially 
to  the  physiologist  and  the  enlisted  man  taking-  pulse  and  blood 
pressure,  who  should  promptly  report  to  the  clinician  any  note- 
worthy change  in  these  observations  or  in  the  respiration. 

5.  No  test  should  be  prolonged  beyond  the  point  where  the  final 
rating  can  be  determined.     For  example  if  the  subject's  heart  puts 
him  in  class  C  or  D,  it  is  a  matter  of  no  great  interest  whether  he 
ranks  A  or  B  on  the  psychological  test.     It  is  important  that  the 
test  be  so  conducted  that  subjects  will  not  have  the  expectation  in 
advance  of  undergoing  anything  dangerous  or  disagreeable ;  for  this 
reason  tests  should  rarely  be  prolonged  to  the  point  of  fainting,  un- 
consciousness, or  great  discomfort. 

6.  All  members  of  the  unit  must  exercise  diligent  care  to  prevent 
the  prejudicing,  alarming,  or  exciting  of  the  subject.     This  applies 
not  only  to  subjects  being  tested,  but  to  all  fliers  arid  candidates  who 
may  be  later  subject  to  test.     Even  chance  remarks,  which  might 
give  the  impression  that  there  is  danger  or  discomfort  in  the  test, 
or  that  many  men  are  disqualified  as  a  result  of  the  test,  must  be 
scrupulously    avoided.     Unfortunate    remarks    which    seem    unim- 
portant to  the  person  making  them,  do  in  many  cases  produce  such 
an  effect  on  the  subject  that  his  performance  on  the  test  is  materially 
modified. 

7.  Instructions  to  the  aviator  concerning  the  operation  of  the 
psychological   apparatus,  will  be  given  by  the  psychologist  only. 
Additions  by  other  members  of  the  group  are  detrimental. 

8.  During  the  first  three  minutes  of  the  run,  the  aviator  will  be 
coached  by  the  psychologist. 

9.  Stop-watches  of  the  psychologists,  ophthalmologist,  and  car- 
diac observer  will  be  started  simultaneously,  and  all  records  will  be 
kept  in  terms  of  elapsed  time  after  watches  are  started. 

10.  Beginning  at  the  sixth  minute,  and  at  three-minute  intervals 
thereafter,  the  psychological  work  will  be  stopped  for  30  seconds, 
to  allow  the  ophthalmological  and  cardiac  examination.     It  is  im- 
portant that  the  ophthalmologist  keep  track  of  the  time  so  that  he 
shall  be  ready  promptly. 

11.  Full  instructions  as  to  the  ophthalmological  tests  must  be 
given  previous  to  the  commencing  of  the  run,  so  that  no  instructions 
will  be  necessary  in  the  30-second  period. 

12.  In  case  the  clinician  feels  that  the  subject's  physical  condition 
demands  more  frequent  examinations  these  shall  be  made  in  such 
a  way  as  to  disturb  the  psychological  test  as  little  as  possible. 


222  MANUAL   OF    MEDICAL  RESEARCH   LABORATORY. 

13.  Rebreathing  tests  may  be  made  separately  for  the  purposes 
of  the  different  departments,  but  in  rating  fliers  a  single  test  will 
be  made  as  a  routine.     If  it  seems  desirable  an  unsatisfactory  test 
may  be  repeated. 

14.  Results  should  not  be  indicated  to  the  aviator  except  in  the 
most  general  form — especially  to  be  avoided  is  any  statement  of 
"  how  far  he  went "  in  terms  of  thousands  of  feet  altitude.    It  may 
be  made  plain  there  is  no  direct  parallel  between  oxygen  percentage 
in  the  rebreathing  test  and  low  atmospheric  pressure,  and  that  in 
the  rapid  progression  of  the  test  the  results  would  be  very  fallacious 
if  applied  to  active  working  conditions  at  high  altitudes. 

15.  The  duties  of  the  officers  are : 

(a)  The  physiologist  will  have  immediate  charge  of  enlisted  men 
A  and  B,  see  that  their  work  is  being  done  properly,  that  all  appa- 
ratus is  in  order,  and  that  necessary  supplies  are  kept  in  sufficient 
stock.  He  will  take  pulse  and  blood  pressure  before  the  rebreathing 
test  in  the  manner  prescribed  on  page  2  of  the  history.  He  will  pass 
on  the  character  of  the  pulse,  respiration,  and  blood  pressure,  con- 
ferring with  the  clinician  as  to  their  bearing  upon  the  normality 
of  the  circulatory  apparatus.  He  will  enter  this  judgment  on  these 
matters  under  "  summary  "  on  page  2  of  the  history. 

(5)  The  clinician  will  carefully  read  the  history  prepared  by  en- 
listed men  C;  go  into  more  detail  as  to  points  suggested,  especially 
as  to  the  exact  condition  at  time  of  test.  He  will  then  make  a  phys- 
ical examination  and  fill  in  the  entries  on  the  history  form  or  dic- 
tate them.  He  will  be  present  at  each  rebreathing  test,  following 
carefully  the  condition  of  the  subject,  interrupting  the  test  if  he  con- 
siders that  the  subject's  physical  condition  demands  it,  being  the 
one  man  responsible  for  ending  the  experiment.  On  completion  of 
the  test  he  will  enter  on  the  blank  (p.  3)  the  exact  condition  at 
beginning  and  at  close  of  test  (especially  whether  unconscious,  faint- 
ing, etc.),  note  manner  of  recovery,  and  any  other  remarks  as  to 
progress  of  test.  He  will  summarize  on  page  2  the  behavior  of  the 
subject's  general  physical  fitness  both  before  and  during  the  test, 
especially  the  behavior  of  the  heart.  He  will  consult  with  the  phys- 
iologist as  to  respiration,  pulse,  and  blood  pressure. 

(<?)  The  ophthalmologist  will  conduct  preliminary  tests,  and  tests 
during  the  rebreathing  experiment.  He  will  base  his  rating  on  the 
results  of  both  tests. 

(d)  The  psychologist  will  observe  the  performance  of  the  subject 
during  the  test.  He  will  plainly  signal  to  the  clinician  when  he  is 
ready  to  terminate  the  experiment,  and  the  clinician  will  ordinarily 
take  the  subject  off  at  this  time.  He  will  base  his  rating  on  both 
the  preliminary  performance  and  on  performance  under  low  oxygen. 

16.  The  duties  of  the  enlisted  men  are  as  follows : 


MANUAL   OF   MEDICAL  RESEARCH   LABORATORY.  223 

A  will  have  the  care  of  the  rebreathing  machine  during  the  test 
and  will  be  responsible  that  it  is  kept  in  order.  He  will  make 
analyses  and  record  them  on  the  history  sheet,  page  3. 

B  will  take  and  record  pulse  and  blood-pressures  during  the  test 
and  attach  this  record  to  the  history  sheet.  He  will  fill  in  the  names 
at  the  top  of  page  three  of  the  history.  He  will  be  responsible  that 
all  papers  are  taken  to  be  plotted  as  soon  as  above  entries  are  made. 

C  will  receive  candidates,  give  them  directions  as  to  procedure, 
take  their  history,  assist  physiologist  and  clinician  in  their  examina- 
tions. He  will  also  assist  E  with  copying  and  keeping  in  order 
the  histories. 

D  will  be  responsible  for  making  three  copies  of  the  charts  in 
each  case. 

E  will  be  clerk,  writing  such  letters,  etc.,  as  may  be  ordered,  and 
being  responsible  that  three  identical  copies  of  each  record  are  pre- 
pared, and  that  they  are  mailed  after  approval  to  their  appropriate 
destinations. 

F  will  have  charge  of  the  psychological  apparatus  and  will  man- 
ipulate the  lights  during  the  test.  He  will  assist  in  the  plotting  and 
copying. 

17.  The  Commanding  Officer  of  the  unit  may  readjust  the  assign- 
ments of  the  enlisted  men  as  he  deems  wise ;  e.  g.,  A  and  B  should  be 
interchangeable,  and  it  may  be  necessary  that  C,  D,  and  E  assist  each 
other  somewhat. 

ROUTINE   FOR   RECORD    KEEPING. 

1.  Candidates  will  report  lo  enlisted  man  C. 

2.  C  will  enter  candidate's  name  in  the  journal,  take  the  history 
and  attach  to  it  the  check  slip.    The  history  (original  copy)  will  be 
either  written  in  ink  or  typewritten.    The  two  copies  will  be  type- 
written.    Entries  by  the  various  departments  are  to  be  made  only 
on  the  original  and  the  original  is  to  be  signed  by  each  officer,  military 
rank  being  added  and  designation  as  "  Physiologist,"  etc. 

3.  Each  step  afterwards  is  to  be  initialed  on  the  check  slip  as  it  is 
made. 

4.  Preliminary  pulse  and  blood  pressures  to  be  taken  by  the  physi- 
ologist. 

5.  Physical  examination  to  be  made  and  entered  (or  dictated)  by 
clinician. 

6.  Preliminary  eye  examination  made  and  entered  by  ophthal- 
mologist. 

7.  History  to  go  to  rebreathing  room  with  the  subject,  to  be  de- 
livered to  B.     B  is  to  be  instructed  that  no  test  is  to  proceed  until  the 
history  is  in  his  hands  and  until  all  procedures  up  to  this  point  are 
checked  on  the  check  slip. 


224  MANUAL   OF   MEDICAL  RESEARCH   LABORATORY. 

8.  At  the  close  of  the  test  the  names  of  observers  are  to  be  entered 
by  B ;  any  remarks  about  the  test  may  be  entered  by  the  physiologist 
or  the  clinician ;  the  clinician  will  enter  condition  at  beginning  and 
close  of  experiment  and  at  this"  time  he  will  usually  enter  his  remarks, 
under  the  summary  on  page  2.    The  air  analyses  will  be  entered  by 
B,  who  obtains  them  from  A,  as  well  as  the  exact  time  of  day  and  the 
duration  of  the  test. 

9.  At  the  close  of  the  test  all  papers  (history,  check  slip,  pulse  and 
pressure  notes,  duplicate  of  psychologist's  notes,  kymograph  tracing) 
are  pinned  together  and  taken  to  plotting  room  by  B,  and  placed  in 
folder  marked  "  Plotting  room.    To  be  plotted." 

10.  Three  identical  plots  are  made  by  D. 

11.  D  takes  all  papers  to  ophthalmologist's  desk  and  places  them 
in  folder  marked  "  Ophthalmologist.    For  notes  on  histories."    Oph- 
thalmological  data  are  to  be  added  to  chart  and  entries  made  under 
summary  on  page  2. 

12.  Papers  taken  in  turn  to  similar  folders  on  desks  on  psycholo- 
gist, physiologist,  and  clinician,  who  similarly  make  their  additions 
to  chart  and  history. 

13.  Each  department  should  attend  to  this  clerical  work  as  expe- 
ditiously  as  possible,  and  see  that  papers  are  forwarded  at  once  to 
the  next  department. ' 

14.  When  notations  are  complete  all  papers  are  to  be  placed  in 
basket  on  C's  desk  marked  "  Examination  complete.    Plotted.    Notes 
made.    To  be  rated." 

15.  A  conference  of  all  officers  on  rating  is  to  be  held  at  frequent 
intervals,  preferably  each  day.    The  rating  is  decided  on  concensus 
of  opinion,  being  ordinarily  the  lowest  rating  of  any  department. 
The  subject  is  to  be  assigned  to  one  of  four  classes,  viz:  A  (no  re- 
striction as  to  altitude),  B    (should  not  fly  above  15,000  feet),  C 
(should  not  fly  above  8,000  feet),  and  D   (should  not  fly  at  all). 
Further  recommendations  of  the  board  in  greater  detail  will  at  this 
time  be  dictated. to  E,  who  will  later  see  that  such  entry  is  made.    It 
is  desired  that  recommendations  be  made  as  explicit  and  detailed  as 
possible,  advising  as  to  the  exact  kind  of  work  the  subject  can  do  best. 

Entries  under  recommendations  of  the  board  should  be  made  in 
language  understandable  to  the  laity.  (In  the  rest  of  the  report  this 
is  not  important  since  the  data  is  primarily  for  reference  on  repeat 
examinations  or  for  collation.)  The  definite  figures  established  as 
to  altitude  are  to  be  given  as  above.  It  is  a  good  usage  to  explain 
by  a  phrase  or  so  all  ratings  below  A.  For  instance,  if  the  psychol- 
ogist gives  a  rating  of  B,  the  following  phraseology  may  be  em- 
ployed: "  Class  B  (should  not  fly  above  15,000  feet),  becomes  ineffi- 
cient before  highest  altitudes  are  reached."  In  case  of  heart  strain : 


MANUAL  OF   MEDICAL  EESEAECH   LABORATORY.  225 

"  Class  C  (should  not  fly  above  8,000  feet).  Preserves  his  efficiency 
at  moderate  altitudes  only  at  the  cost  of  severe  heart  strain.  Would 
wear  out  soon  if  used  at  high  altitudes,"  etc. 

1<5.  Records  to  be  returned  to  basket  marked  "  Rated.     To  be 
copied." 

17.  E  will  see  that  three  copies  are  prepared,  identical,  except  that 
only  the  original  need  be  signed.    He  will  then  return  them  to  basket 
marked  "  Copied.     To  be  inspected." 

18.  Reports  will  receive  final  inspection  of  Commanding  Officer 
of  unit,  whereupon  E  will  send  the  original  to  the  Commanding  Offi- 
cer of  the  flying  field,  one  copy  to  office  of  the  Surgeon  General, 
United  States  Army,  and  one  will  be  filed  in  the  Medical  Research 
Laboratory.     (For  the  present  all  three  copies  and  all  other  papers 
will  be  sent  to  the  Medical  Research  Laboratory  at  Mineola,  where 
they  will  be  inspected  and  distributed  as  above.    When  this  is  done, 
it  will  be  advisable  for  the  unit  to  keep  on  file  duplicates  of  the  origi- 
nal notes.     When  the  original  is  sent  direct  to  the  Commanding  Offi- 
cer of  the  flying  field  and  is  thus  on  file  at  the  field,  the  unit  will  not 
need  duplicates.) 

19.  In  filing  records  in  Medical  Research  Laboratory  each  one  as 
it  arrives  will  be  given  a  serial  number  and  all  papers  marked  with 
this  number  placed  in  a  manila  folder  also  marked  with  name  and 
number,  and  filed  serially.    A  smaller  (3  by  5)  card  will  be  made 
out  for  each  record  and  kept  in  a  smaller  file  in  alphabetical  order. 

20.  In  case  the  examination  has  not  been  completed,  the  records 
will  be  kept  in  basket  marked  "  Examination  incomplete.    To  return." 

21.  When  it  is  evident  that  an  examination  will  never  be  com- 
pleted (e.  g.,  if  aviator  is  moved  to  another  station),  the  history  will 
be  filed,  not  with  the  completed  histories,  but  in  a  separate  division 
arranged  alphabetically  marked  "  Incomplete.    Will  not  return."    A 
small  card  (3  by  5)  will  be  made  out  for  such  a  record  and  will  be 
filed  with  the  other  small  cards^ 

22.  Incomplete  records  on  which  no  rating  has  been  made  will  not 
be  sent  to  the  Commanding  Officer  at  aviation  field  nor  to  the  Chief 
Surgeon,  but  will  be  kept  by  the  unit  unless  the  aviator  has  been 
transferred  when  they  should  be  sent  to  the  Mineola  Laboratory. 

23.  Any  correspondence  relative  to  an  aviator  is  to  be  filed  with 
the  other  reports  at  Mineola. 

DIRECTIONS    TO    CLINICIAN    AS    TO    CONDUCT   OF    REBREATHING    TEST. 

The  clinician  is  to  be  present  throughout  the  test  and  is  primarily 

responsible  for  the  subject's  condition.     It  will  almost  always  be 

possible  to  keep  sufficiently  accurate  track  /of  the  heart  action  by 

listening  during  the  eye  examination  in  order  to  avoid  interference 

89119—18 15 


226  MANUAL  OP  MEDICAL  RESEAECH   LABORATORY. 

with  the  psychological  test.  In  case  the  safety  of  the  subject  demands 
it,  however,  he  should  not  hesitate  to  examine  the  heart  more  fre- 
quently, especially  toward  the  close  of  the  test. 

The  clinician  will  be  the  one  to  terminate  the  test  by  removing 
the  mouthpiece  or  nose  clip.  About  four  times  out  of  five  probably 
this  will  be  at  the  instance  of  the  psychologist,  who  will  plainly 
indicate  as  soon  as  his  results  are  satisfactory.  When  this  point  has 
been  reached  the  subject  is  probably  within  a  short  space  of  insensi- 
bility and  the  mouthpiece  should  be  removed  without  delay. 

The  clinician  may  terminate  the  test  before  the  psychologist  has 
got  his  full  results  if  he  considers  that  safety  demands  it,  but  ^uch 
an  occurrence  should  be  infrequent  if  proper  judgment  is  used,  be- 
cause any  abnormal  circulatory  condition  will  give  an  early  psycho- 
logical effect  and  it  is  usually  safe  to  let  the  test  go  to  this  point. 
An  exception  is  any  case  of  cardiac  arrhythmia  (except  sinus  ar- 
rhythmia), which  increases  during  the  test.  In  this  case  the  experi- 
ment should  be  terminated  very  early  from  the  possibility  of  ven- 
tricular fibrillation. 

When  a  definite  cardiac  lesion  can  be  determined  it  is  unnecessary 
to  prolong  the  test,  for  if  the  clinician's  rating  is  C  or  D  it  is  a  mutter 
of  small  importance  whether  the  psychologist's  rating  is  A  or  B. 

The  physiologist  may  suggest  terminating  the  test  if  something  is 
manifestly  wrong,  as  e.  g.,  with  the  apparatus. 

The  indications  for  interference  by  the  clinician  are  two:  First, 
that  he  has  determined  a  disqualifying  cardiac  condition;  second, 
that  the  subject  is  on  the  verge  of  fainting.  To  guard  against  this 
latter  the  clinician  should  carefully  watch  the  pulse  and  blood- 
pressure  record  and  should  instruct  the  observer  to  call  his  attention 
at  once  to  any  marked  change.  Blood-pressure  readings  every  minute 
are  desirable  toward  the  end  of  the  test.  Subjects  who  have  had  an 
excessive  response  in  pulse  and  blood  pressure,  those  whose  hearts 
are  evidently  working  too  hard  throughout  the  test  should  be  espe- 
cially carefully  watched,  but  even  in  these  cases  it  is  always  safe  to 
allow  the  test  to  go  on  either  until  the  psychologist  is  satisfied  or 
until  there  are  definite  signs  of  fainting.  Eapidity  in  pulse  or  mod- 
erate increase  in  blood  pressure  is  not  an  indication  for  stopping 
the  test. 

The  first  sign  of  fainting  will  be  a  sudden  drop  in  diastolic  pres- 
sure, followed  latter  by  a  drop  in  systolic  pressure,  then  a  drop  in 
pulse.  It  is  often  possible  to  remove  the  mouthpiece  when  the  dias- 
tolic fall  has  occurred,  but  before  the  other  two.  A  slow  and  steady 
decrease  in  diastolic  pressure  is  to  be  regarded  as  normal  if  not 
excessive,  especially  when  the  systolic  pressure  is  not  increasing,  but 
such  a  steady  decline  frequently  ends  with  a  sudden  fall  and  demands 
careful  watching  from  minute  to  minute. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  227 

It  is  highly  important  to  avoid  fainting  when  possible  (and  even 
the  cerebral  type  of  unconsciousness),  though  a  certain  number  of 
cases  will  faint  in  spite  of  the  most  careful  watching ;  this  may  occur 
with  great  suddenness,  especially  when  coming  early  in  the  run. 

A  middle  ground  must  be  taken,  giving  the  psychologist  as  much 
opportunity  as  possible  for  his  observations  and  yet  avoiding  dis- 
agreeable terminations  of  the  test.  As  remarked  above,  the  psycholo- 
gist should  terminate  the  test  at  least  four  times  out  of  five. 

DIRECTIONS  FOR  CLINICIAN  AS  TO  RATING. 

When  a  diagnosis  of  valvular  lesion  of  the  heart  can  be  made,  no 
matter  how  well  compensated,  the  subject  should  be  disqualified. 
Rarely  in  the  case  of  a  man  who  has  already  qualified  as  a  pilot  and 
where  the  compensation  is  excellent  and  the  reaction  to  the  test  good, 
he  may  be  passed  in  class  C  with  explicit  directions  that  he  be  very 
carefully  watched  and  be  withdrawn  later  from  all  air  work  if  he 
gives  any  evidence  of  wearing  badly. 

Subjects  who  have  or  develop  arrhythmia  are  to  be  rejected  (except 
sinus  arrhythmia,  which  is  of  no  importance). 

Subjects  who  show  deterioration  of  heart  sounds  (usually  due  to 
poor  arteries,  fatty  heart,  or  flabby  heart  muscle)  should  be  rejected, 
or  if  the  deterioration  develops  late  in  the  test,  be  rated  in  class  C. 

In  any  of  the  above  cases  the  experiment  should  not  be  prolonged 
beyond  the  point  where  the  clinician  has  fully  satisfied  himself  of  an 
abnormal  heart. 

The  clinician  will  not  be  called  upon  to  decide  on  cases  who  com- 
pensate poorly,  since  they  will  receive  a  low  rating  from  the  psycholo- 
gist, who  will  demonstrate  failure  of  compensation  long  before  the 
clinician  could.  The  type  of  person,  however,  who  because  of  gen- 
erally poor  constitution  fails  to  compensate  at  all  (no  rise  in  pulse, 
none  in  respiration,  no  change  in  blood  pressure),  should  be  rejected 
rather  than  given  a  low  rating.  Such  cases,  however,  should  be  very ' 
rarely  found  in  the  Aviation  Service. 

Of  the  cases  who  compensate  well  (probably  75  per  cent  or 
more  of  the  experiments)  the  rating  should  be  based  on  the  amount  of 
circulatory  strain  involved  in  maintaining  compensation. 

It  is  difficult  to  establish  fixed  rules  in  this  regard  and  much  must 
be  left  to  the  judgment  of  the  examiner.  Those  who  become  uncon- 
scious at  less  than  8  per  cent  oxygen  without  circulatory  failure,  of 
course,  deserve  an  A  rating.  We  have  passed  a  few  subjects  who  had 
a  circulatory  collapse  (either  fainting  outright  or  marked  drop  in 
diastolic  pressure)  at  less  than  8  per  cent.  Those  whose  circulation 
fails  between  8  and  10  per  cent  may  be  rated  B,  and  those  above  10 
per  cent  C.  If  in  doubt,  it  is  safer  to  give  a  lower  rating,  since  more 
fliers  will  be  needed  for  lower  than  for  higher  altitudes,  and  the 


228  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

late  effects  of  circulatory  strain  are  always  to  be  considered — i.  e., 
the  early  development  staleness.  Eating  should  be  very  conserva- 
tive in  cases  of  high  blood  pressure.  If  this  is  above  150,  the  rate 
should  be  B ;  if  maintained  above  160,  it  should  be  C,  especially  when 
there  is  evidence  of  circulatory  fatigue.  The  paragraphs  on  blood 
pressure  in  the  directions  to  the  physiologist  should  be  carefully 
followed. 

In  cases  given  a  low  rating  on  account  of  circulatory  strain,  the 
fact  should  be  made  evident  under  "  recommendation  of  the  board  " 
on  the  report.  Some  such  phraseology  as  the  following  may  be 
employed:  "Class  C  (should  not  fly  above  8,000  feet).  Maintains 
his  efficiency  at  moderate  altitudes  only  at  the  cost  of  severe  heart 
strain.  Would  quickly  wear  out  if  used  at  high  altitudes." 

NOTES  ON   THE   DIAGNOSIS   OF  VALVULAR   HEART  DISEASE. 

The  cases  of  valvular  disease  which  the  clinician  of  the  research 
board  will  have  to  decide  will  almost  always  be  difficult  to  diagnose. 
This  is  because  the  candidates  have  been  already  carefully  examined 
and  selected. 

The  rebreathing  test  is  a  very  efficient  aid  to  the  more  usual  methods 
of  examination,  and  it  may  pretty  safely  be  asserted  that  a  man  who 
makes  a  good  run  on  this  apparatus  can  have  no  serious  cardiac 
lesion. 

Overemphasis  must  not  be  placed  upon  single  factors.  This  is 
especially  true  of  murmurs.  Systolic  murmurs  are  extremely  com- 
mon, especially  when  heard  at  the  base,  in  cases  where  there  is  no 
organic  disease.  Roughnesses  of  the  first  sound  that  suggest  a  slight 
thrill  are  also  not  uncommon. 

A  clear  prolonged  diastolic  murmur  is,  of  course,  almost  certainly 
caused  by  either  aortic  insufficiency  or  mitral  stenosis,  but  even  in 
this  case  a  diagnosis  must  not  be  based  on  the  murmur  alone.  Evi- 
dence of  hypertrophy  and  dilatation,  either  or  both,  should  be  present, 
and  in  mitral  cases  a  pretty  marked  accentuation  of  the  pulmonic 
second  sound.  The  trained  ear  learns  to  judge  from  the  character 
of  the  heart  sounds  rather  than  the  murmurs  whether  there  is  organic 
disease  or  not,  but  it  is  difficult  to  express  in  words  just  what  the 
changes  in  the  heart  sounds  are  which  prove  decisive. 

A  heart  with  an  organic  lesion  seems  to  behave  in  one  of  two  ways 
on  the  low  oxygen  test.  It  may  fail  to  compensate  almost  from  the 
start ;  in  this  case  there  may  be  no  accentuation  of  the  first  sound  nor 
of  the  murmurs,  but  rather  a  deterioration  of  the  sounds  and  a 
shortening  of  the  first  interval.  Such  a  subject  will  probably  become 
inefficient  very  early,  will  get  very  blue,  and  be  extremely  uncom- 
fortable ;  a  number  have  themselves  removed  the  mouthpiece  saying 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  229 

they  felt  that  they  were  suffocating.    This  type  of  reaction,  indicat- 
ing poor  heart  muscle,  will  be  rarely  found  among  aviators. 

Much  the  commoner  type  of  reaction  is  that  of  excellent  compensa- 
tion or  rather  of  overcompensation.  In  this  the  heart  is  evidently 
on  a  heavy  strain  from  the  start,  the  sounds  loud  and  booming,  the 
apex  impulse  heaving,  second  sounds  accentuated.  Murmurs  are 
sure  to  come  out  much  more  clearly.  For  a  reason  which  is  difficult 
to  understand,  this  type  of  case  usually  runs  a  high  blood  pressure, 
140  to  160,  occasionally  even  to  180.  Psychological  efficiency  is  often 
held  very  well. 

Such  well-compensated  hearts  frequently  hold  out  and  do  their 
work  against  the  odds  up  to  a  very  high  altitude.  When  a  diagnosis 
of  valvular  lesion  is  clear,  however,  it  would  be  unwise  to  prolong 
the  test  to  the  point  of  cardiac  failure,  as  the  latter  would  involve 
much  greater  risk  than  in  the  case  of  the  normal  man. 

Numerous  cases  have  been  observed  where  puzzling  murmurs  have 
been  present  on  preliminary  examination,  which  did  not  become 
stronger  during  the  test,  or  even  disappeared;  in  these  cases  the 
whole  course  of  the  test  was  normal,  there  was  no  evidence  of  cardiac 
incompetence  nor  of  overstrain.  In  such  a  case  the  murmur  should 
have  no  weight  at  all  in  assigning  the  final  rate. 

While  we  feel  very  strongly  on  the  danger  of  flying  to  a  man  with 
valvular  disease,  there  is  bound  in  every  case  to  be  bitter  disappoint- 
ment and  dissatisfaction  with  the  ruling  of  the  board.  For  this  rea- 
son great  care  must  be  exercised  in  the  diagnosis  and,  when  possible, 
two  competent  clinicians  should  argue  on  the  matter.  Usually  it  is 
best  to  repeat  the  test  to  be  absolutely  sure. 

.  Probably  the  chief  source  of  doubt  will  come  from  cases  of  poor 
condition  from  other  causes  (bad  cold,  diarrhea,  etc.)  with  func- 
tional murmurs.  In  some  of  these  cases  an  interval  of  two  weeks 
before  a  retest  will  clear  up  the  confusion.  In  the  other  cases  it  may 
be  necessary  to  have  a  more  thorough  inquiry  into  the  general  con-, 
dition  at  the  post  hospital  or  even  at  a  base  hospital. 

In  case  of  doubt  it  is  safe  to  err  on  the  side  of  protecting  the  man, 
especially  when  he  is  a  candidate  or  a  cadet.  In  case  of  a  finished 
pilot  he  may  be  passed  in  class  C  when  there  is  a  reasonable  doubt, 
but  the  recommendation  of  the  board  should  contain  explicit  direc- 
tions that  his  heart  must  be  very  carefully  watched,  and  that  he  is 
to  be  withdrawn  from  flying  if  trouble  develops.  The  case  should 
be  called  to  the  attention  of  the  Flight  Surgeon  and  the  man  himself 
should  understand  the  situation  thoroughly — both  his  own  condition 
and  the  danger  of  aviation  to  a  defective  heart. 


230  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

ROUTINE  EYE  EXAMINATION    DURING  REBREATHING  TEST. 

1.  Instruct  the  candidate  fully  as  to  the  methods  of  procedure  dur- 
ing the  rebreathing  experiment  and  the  signs  that  he  will  make  to 
tell  you  when  his  vision  is  blurred,  when  he  is  diplopic,  etc.     It  is 
well  to  take  time  to  instruct  the  candidate  in  this  way  so  that  valu- 
able time  may  not  be  lost  during  the  experiment,  and  the  psycho- 
logical reaction  disturbed  as  little  as  possible. 

2.  Beginning  of  sixth  minute,  after  start  of  rebreathing  experi- 
ment, note   (a)   convergence  near  point;    (&)    accommodation  near 
point;  (c)  field  of  binocular  fixation. 

3.  Note  convergence,  accommodation,  and  field  of  binocular  fixa- 
tion during  first  30  seconds  of  every  third  minute,  and  vision  every 
6  minutes. 

4.  Make  at  least  one  reading  after  candidate  is  removed  from  ap- 
paratus. 

5.  Make  note  of  reason  for  removing  man  from  rebreathing  ap- 
paratus on  face  of  card. 

6.  Note  also  on  face  of  card  whether  man  is  apparently  a  desir- 
able candidate  as  far  as  the  eyes  are  concerned. 

7.  All  records  must  be  in  ink. 

8.  Make  all  notes  on  5  by  8  history  card.    Loose  papers  are  un- 
desirable. 

9.  Make  a  record  of  the  examination  in  the  cross  file  imder  head- 
ing "  Tests  and  date." 

10.  As  soon  as  oxygen  percentage  is  recorded,  rate  the  candidate 
under  the  date  in  this  manner,  on  the  back  of  the  5  by  8  card : 

(1)  11  per  cent  (per  cent  of  oxygen  at  which  first  permanent  change  occurs). 

(2)  7  per  cent  (per  cent  of  oxygen  where  the  candidate  is  ocularly  inefficient 
from  any  cause).    Eye  (A). 

Thus:  4-20-18.    (1)  11  per  cent.    (2)  7  per  cent.    Eye  (A). 
N.  B. — Make  notes  of  rating  c,  b,  c,  or  d  on  card  for  tests  and  dates  after 
man's  name. 

11.  As  soon  as  data  is  complete  to  this  point,  enter  it  on  the  three 
copies  of  the  history  and  make  any  necessary  recommendation,  stat- 
ing why  it  is  made. 

(a)  Under  summary  of  observations  during  low  oxygen  tension 
test,  use  scientific  terms. 

(Z>)  Under  recommendation  of  board,  use  lay  expressions. 

One  copy  of  the  history  is  sent  to  the  Post  Commander,  one  to  the 
Medical  Research  Laboratory,  Hazelhurst  Field,  Mineola,  L.  I.,  and 
one  to  Air  Service  Division,  Surgeon  General's  Office,  Washington, 
D.  C. 

12.  Make  certain  that  the  5  by  8  card  which  is  retained  in  the 
laboratory  gives  a  complete  statement  of  the  reason  why  a  candidate 
was  rated  <z,  6,  c,  or  d,  and  what  recommendations  were  made  as  to  his 
final  disposition. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  231 

13.  Keep  4  by  6  cross  file  up  to  date,  following  some  such  scheme: 

Index  (cross  scheme  for  Ophthalmological  Department). 

Card  color  scheme:  (1)  yellow,  (2)  blue,  (3)  salmon,  (4)  white. 
Subindex  under    (a)  Rebreathing. 

(b)  Name  and  date  and  altitude  in  feet  where  break  was  first  shown. 

(1)  Men  who  have  flown.     FLIERS.     (1)  Pilot.  (a)  Have  flown. 

(2)  Observer.     (6)  Have  not  flown. 

(2)  Acclimated. 

(3)  Men  who  show  break  in  accommodation ACCOMMODATION. 

(4)  Men  who  show  break  in  convergence CONVERGENCE. 

(5)  Men  who  (do  or  not)  show  break  after  abuse  of  alcohol,  insuf- 

ficient sleep,  sex  excess,   (a)  Yes.  J DISSIPATION. 

(6)  Muscles MUSCLES. 

(7)  Men  who  show  no  ocular  break NORMAL. 

(8)  Break  in  field  of  fixation FIXATION. 

(9)  Refractive  errors  (break  or  not),   (a)  Yes.  j REFRACTION. 

(10)  Men  show  break  in  vision,     (a)  Acuity  of) 

(6)  Color        \ VISION. 

(c)  Field  of    J 

(11)  Men  who  (do  or  not)  show  break  after  illness ILLNESS. 

(12)  Men  who  (do  or  not)  show  break  after  typhoid  vaccination. 

(a)  Yes.l  TvpHom 

(6)  No.  / IYPHOID. 

(13)  Oxygen  given  during  experiment OXYGEN. 

(14)  Stereoscopic  vision STEREOSCOPE. 

(15)  Retinal  sensitivity,     (a)  Contrast.    \  T».,_ 

(6)  Treshold.   / KETINA. 

(16)  Tension  (Intraocular) TENSION. 

(17)  Men  who  have  had  accidents ACCIDENTS. 

^18)  Men  who  are  stale STALENESS. 

ROUTINE  MONTHLY  EXAMINATION  OF  THE  EYE  OF  THE  FLIER  (SUGGESTED). 

A  record  of  the  completed  609  examination  should  be  kept  with  the 
papers  of  each  flier,  with  the  additional  record  of  the  near  point  of 
convergence  and  muscle  strength  finding. 

1.  Visual  acuity :  If  the  visual  acuity  has  altered,  ophthalmoscopic 
examination  should  be  made  to  determine  the  cause. 

2.  Examination  of  the  eye. 

3.  Muscle   balance,      (a)  If   change   in   findings,   record   muscle 
strength. 

4.  Near  point  of  accommodation. 

5.  Near  point  of  convergence. 

N.  B. — If  alteration  is  found  in  any  of  the  above  findings,  stereo- 
scopic vision  should  be  tested. 

OPHTHALMOLOGICAL  EQUIPMENT   FOR  BRANCH  LABORATORIES. 

1.  Two  small  millimeter  rules,  15  centimeters  in  length. 

2.  One  Prince  rule.    Illiterate  "  Es  "  as  test  object. 


232 


MANUAL  OP   MEDICAL  KESEAECH   LABOBATOKY. 


3.  One  5-foot  centimeter  rule,  marked  in  millimeters,  and  in  de- 
greees  of  tangents  of  arc. 

4.  One  Hare-Marple  battery-handle  electric  ophthalmoscope. 

5.  Two  dozen  batteries  and  three  extra  lamps  for  the  ophthalmo- 
scope. 

6.  One  stop  watch. 

7.  One  Schweigor  hand  perimeter,  with  two  extra  eyepieces,  one 
for  monocular  use  and  one  for  binocular  use. 

8.  Three  75-watt,  110-volt,  nitrogen  daylight  lamps. 

9.  Two  extension  brackets,  with  two  shades. 

10.  One  set  of  visual  acuity  test  cards.     (Black's,  F.  A.  Hardy  & 
Co.) 

11.  Trial  case  No.  4072,  with  a  multiple  Maddox  rod  and  1^-inch 
lens. 

12.  Trial  frame  No.  4157. 

13.  One  box  square  prisms  No.  4112. 

14.  Jenning's  color-test  No.  1. 

15.  Keeves's  wedge. 

Per  cent  transmission  and  density  of  average  wedge. 


Millimeters  

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

Density  

0.225 

0.466 

0.70 

0.915 

1.14 

1.39 

1.62 

1  86 

3  085 

2  30 

Per  cent  transmission  

59.74 

34.28 

19.84 

12.14 

7.20 

4.06 

2.40 

1  38 

83 

50 

Millimeters  

55 

CO 

65 

70 

75 

80 

85 

90 

95 

100 

Density  

2.57 

2.785 

3.0 

3.28 

3.485 

3.72 

3.945 

4  18 

4  42 

4  65 

Percent  transmission  

.26 

.16 

.1 

.05 

.03 

.02 

.01 

.006 

003 

.001 

16.  Two  retinoscopes,  with  an  18  millimeter  plane  mirror. 

17.  One  36-watt,  110-volt,  frosted  bulb,  Edison  Mazda  lamp. 

18.  One  iris  diaphragm  on  stand  (deZeng). 

19.  Opaque  shades  for  examining  room. 

20.  One  5  by  8  filing  drawer  and  500  No.  1  cards  and  500  No.  2 
cards,  with  alphabetical  index  guides. 

21.  One  4  by  6  filing  drawer,  50  yellow  tabbed  cards,  100  blue 
tabbed  cards,  150  salmon  tabbed  cards,  and  300  plain  white  ruled 
cards. 

22.  Copy  of  per  cent  transmission  and  density  for  average  wedge. 

23.  Copy  of  cross-filing  scheme  for  ophthalmological  records. 

24.  Charts  for  recording  the  field  of  vision,  100. 

25.  Charts  for  recording  field  of  binocular  fixation,  100. 

26.  Jaeger  test  type,  6  sets. 

27.  Reeves  contrast  sensitivity  test  object. 

28.  One  sterescope  and  2-A,  2-B,  and  2-C  cards. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  233 

The  board  requests  that  a  full  report  of  the  work  of  the  branch 
laboratories  be  made  once  a  month. 

The  ophthalmologists  at  the  branch  laboratories  will  be  expected 
to  do  all  the  research  work  possible,  keeping  the  problem  of  the  stale 
aviator  in  mind  and  examining  men  who  have  had  an  accident  or 
are  having  difficulty  in  flying  or  landing.  A  letter  should  be  sent 
weekly  to  the  central  laboratory  at  Hazelhurst  Field,  Mineola,  L.  L, 
to  the  officer  in  charge  of  the  Ophthalmological  Department,  report- 
ing the  progress  of  the  ophthalmological  work,  giving  details  of 
special  examinations  made  and  any  suggestions  for  improving  the 
work. 

INSTRUCTIONS  TO  THE  PSYCHOLOGIST. 

1.  The  reactor  is  given  the  printed  instruction  sheet,  which  he  is 
instructed  to  read  carefully,  while  care  is  taken  to  avoid  distracting 
his  attention.    During  the  reading  the  psychologist  should  be  ready 
to  explain  any  detail  of  the  apparatus  or  method  in  which  the 
reactor  may  show  interest;  and  after  the  reactor  has  finished,  the 
psychologist  further  explains  the  procedure  and  verbally  emphasizes 
the  important  points  in  the  instruction. 

2.  As  soon  as  rebreathing  commences,  the  reactor  begins  to  respond 
to  the  three  sets  of  stimuli  as  presented  by  the  apparatus  under  the 
manipulation  of  the  psychologist.    During  the  first  three  minutes  of 
the, test  the  psychologist  shall  coach  the  reactor,  if  necessary,  and 
estimate  his  comprehension  composure   (freedom  from  excitement 
or  nervousness),  entering  these  on  the  record  sheet  then  or  later  as 
good,  fair,  or  poor.    He  should  also  note  the  motor  tendencies  of  the 
reactor,  and  if  these  fall  in  one  or  more  of  the  conventional  cate- 
gories, this  also  should  be  entered. 

In  addition  to  these  general  tendencies,  it  is  important  that  the 
psychologist  take  notice  of  the  specific  tendencies  shown  by  the 
reactor,  and  if  definite  types  of  error  are  shown,  watch  during  the 
succeeding  five  or  six  minutes  for  improvements  in  these  details. 

Normally,  the  test  continues  until  complete  inefficiency  is  reached, 
at  which  point  the  psychologist  must  sharply  notify  the  responsible 
medical  attendant  in  order  that  the  reactor  may  at  once  be  given 
air,  and  so  prevented  from  undergoing  the  collapse  which  would 
ensue  in  a  minute  or  so. 

3.  The  psychologist  will  record  the  typical  change  in  the  reactor's 
behavior,  using  the  symbols  which  are  given  on  the  "  symbol  sheet," 
so  that  the  recording  will  interfere  as  little  as  possible  with  the 
observing.    After  the  test  is  ended,  the  entries  on  the  record  sheet 
must  be  at  once  completed. 

4.  Beginning  at  the  sixth  minute,  and  at  three-minute  intervals 
thereafter,  the  psychological  work  will  be  stopped  for  30  seconds  to 


234  MANUAL  OP  MEDICAL  BESEABCH   LABOBATOBY. 

allow  the  ophthalmological  and  cardiac  examination.  It  is  im- 
portant that  the  ophthalmologist  keep  track  of  the  time  so  that  he 
shall  be  ready  promptly. 

5.  The  psychologist  should  endeavor  tactfully  to  remind  the  re- 
actor as  to  the  general  conditions  of  the  test,  particularly  to  remove 
or  avoid  the  impression  that  the  performance  required  is  very  diffi- 
cult.   Especial  pains  should  be  taken  to  restore  the  reactor's  com- 
posure if  he  has  previously  been  stirred  up  by  a  psychoanalytic  or 
other  intimate  personal  inquisition. 

6.  All  members  of  the  unit  must  exercise  caution  that  the  reactor 
shall  overhear  no  remarks,  serious  or  jocular,  concerning  the  diffi- 
culties, danger,  results,  or  other  features  of  the  test  which  might 
excite  him  or  cause  apprehension  or  concern.    Trivial  remarks  fre- 
quently have  a  serious  effect. 

INSTRUCTIONS  TO  THE  PHYSIOLOGIST  AS  TO  THE  REBREATHINQ  TEST. 

It  is  the  physiologist's  duty  to  provide  dependable  conditions  for  a 
rebreathing  experiment.  All  interpretations  of  data  obtained  and 
the  final  rating  of  a  candidate  require  that  the  oxygen  percentage 
during  and  at  the  end  of  a  test  be  accurately  known.  The  analysis 
of  the  air  in  the  tank  at  the  close  of  a  test  must  be  exact.  In  order 
to  have  reliable  analysis  the  gas  analysis  apparatus  must  be  clean  and 
the  samples  of  air  carefully  taken. 

A  perfect  experiment  requires  that  the  rebreathing  machine  be  in 
perfect  order.  Leaks  of  water  and  air  into  and  from  the  machine 
must  be  avoided.  Water  may  be  flowing  into  the  tank  during  an 
experiment  through  the  inlet  valve  either  because  it  is  not  perfectly 
closed  or  is  out  of  repair.  Water  may  be  escaping  through  the  out- 
let valve  for  the  same  reasons.  Leaks  of  air  may  be  due  to  faulty  or 
improperly  closed  valves  or  to  loose-fitting  mouth  parts.  Occasion- 
ally a  candidate  may  be  found  who  sucks  in  air  and  allows  it  to  es- 
cape by  not  keeping  his  lips  closed  around  the  rubber  mouthpiece. 

The  movement  of  air  through  the  rebreathing  machine  must  be 
free  so  that  the  breathing  of  the  candidate  is  not  hampered.  It  is 
necessary  to  test  frequently  the  resistance  offered  by  the  absorption 
cartridge. 

The  physiologist  is  also  responsible  for  the  obtaining  and  the  inter- 
pretations of  all  physiological  data.  These  data  for  the  present  in- 
clude the  frequency  and  volume  of  breathing,  the  pulse  rate,  and  the 
three  arterial  pressures — systolic,  diastolic,  and  pulse. 

The  respiration  data  are  obtained  from  the  kymograph  record  of 
the  spirometer's  movements.  This  record  is  almost  valueless  if  there 
thas  been  leakage  of  water  or  air  during  an  experiment.  The  cali- 
brating of  the  spirometer  and  the  drawing  of  the  scale  should  be 


MANUAL  OF  MEDICAL  RESEARCH   LABORATORY.  235 

accurate  in  order  that  the  per  minute  volume  of  breathing  may  be 
determined  with  exactness.  From  the  varnished  kymograph  tracing 
the  volume  of  breathing  per  minute  is  calculated  for  as  many  sepa- 
rate minutes  as  will  be  found  necessary  in  order  to  determine  the 
curve  of  respiration  throughout  the  experiment.  The  volume  of 
breathing  should  be  calculated  by  the  physiologist  and  the  amount 
and  the  time  of  each  minute-volume  written  down  and  then  handed  to 
the  "  plotter,"  who  will  incorporate  them  in  the  final  record. 

The  so-called  normal  pulse  and  blood  pressures  are  determined 
three  or  four  times  while  subject  sits  at  the  machine  with  nose  clip 
on  and  mouthpiece  in  place.  These  normals  should  be  compared  with 
those  of  the  preliminary  pulse  rate  and  blood-pressure  study.  A 
psychic  influence  should  be  avoided  if  possible.  After  rebreathing 
is  begun  the  pulse  rate  is  counted  every  minute  and  the  arterial  pres- 
sures determined  every  other  minute  until  the  eighteenth  minute,  after 
which  they  are  taken  each  minute  until  the  end  of  the  experiment. 
The  O  space  of  the  record  sheet  should  be  left  blank  and  the  determi- 
nation of  the  first  half  minute  recorded  on  the  line. 

The  rule  to  be  followed  in  making  the  determinations  is  to  count 
the  pulse  rate  in  the  interval  between  20  and  40  seconds  and  to 
record  the  count  on  the  half  minute.  The  first  count,  therefore,  will 
be  recorded  on  the  line  between  0  and  1.  The  systolic  and  diastolic 
pressures  should  be  determined  in  the  interval  between  45  and  15 
seconds  by  the  stop-watch  and  recorded  as  having  been  taken  on 
the  minute.  These  should  be  entered  on  the  record  sheet  in  the  space 
between  the  lines,  the  first  determination  in  space  1.  This  system 
of  recording  will  make  it  possible  for  the  "  plotter "  to  indicate 
the  time  intervals  with  exactness  on  the  chart.  It  is  important  that 
the  exact  time  of  the  termination  of  the  experiment  be  indicated  on 
the  circulation  sheet  so  that  the  man  who  plots  the  record  may 
correctly  indicate  with  a  heavy  line  the  time  the  candidate  was 
taken  off. 

The  physiologist  should  closely  watch  the  respiration  and  circula- 
tion changes  toward  the  end  of  the  test  and  should  inform  the  clin- 
ician when  unfavorable  conditions  develop. 

In  order  that  the  ratings  may  be  just  to  all,  the  volume  of  air 
rebreathed  should  be  large  enough  to  require  30  minutes  to  reduce 
the  oxygen  to  7  per  cent.  To  obtain  uniformity  in  the  rate  of 
oxygen  reduction  the  water  level  in  the  tank  should  be  varied  ac- 
cording to  the  size  of  the  man  to  be  tested.  A  larger  volume  of  air 
is  required  for  a  large  muscular  man  and  a  smaller  volume  than  that 
used  for  the  average  for  a  small  man.  The  physiologist  should  de- 
cide what  level  of  water  in  the  tank  of  the  rebreathing  apparatus 
is  necessary  to  provide  the  requisite  time  for  the  test.  Experience 


236  MANUAL  OF   MEDICAL  RESEARCH   LABORATORY. 

will  soon  make  it  possible  to  adjust  the  volume  satisfactorily  ac- 
cording to  the  size  of  the  candidate  to  be  tested. 

Rating. — When  rating  a  candidate  as  to  physiological  responses, 
take  into  account  the  per  cent  of  oxygen  reached  and  the  time  re- 
quired for  rebreathing.  Ordinarily  a  lower  percentage  will  be 
tolerated  when  the  fall  in  oxygen  is  rapid  and  the  run  short  than 
when  the  fall  in  oxygen  is  slow  and  the  time  long.  If  two  candi- 
dates who  both  endured  down  to  7  per  cent  oxygen,  one  reaching  it 
in  15  and  the  other  in  30  minutes,  are  being  rated  it  would  be  unfair 
to  the  man  who  made  the  longer  run  to  grade  him  on  the  same  basis 
as  that  of  the  short  run.  This  is  the  reason  for  demanding  that  all 
candidates  be  given  a  sufficient  volume  of  air  for  rebreathing  to 
insure  a  run  of  25  to  30  minutes. 

In  rating  take  into  consideration  also  compensation  in  the  breath- 
ing and  circulation.  The  reaction  of  respiration  will  be  recorded  as 
poor,  fair,  good,  or  excessive.  The  majority  of  the  men  examined 
have  shown  at  between  8  and  6  per  cent  of  oxygen,  an  increase  of 
5.5  liters  in  the  volume  of  air  breathed. 

Such  an  increase  is  rated  good,  an  increase  of  15  or  more  liters 
is  regarded  as  excessive.  The  respiratory  response  is  most  marked 
after  12.5  per  cent  of  oxygen  has  been  reached.  The  increase  in  the 
frequency  of  the  pulse  rate  for  the  majority  of  men  who  have  reacted 
well  has  varied  between  20  and  40  per  minute  at  about  8  per  cent  of 
oxygen.  An  acceleration  of  more  than  50  may  be  regarded  as  ex- 
cessive. The  degree  of  acceleration  is  ordinarily  slight  until  the 
oxygen  has  fallen  to  between  13  and  9  per  cent,  but  from  these  down 
the  acceleration  occurs  rapidly.  The  rise  in  systolic  pressure  usually 
is  not  more  than  20  millimeters,  a  greater  rise  is  considered  ex- 
cessive. A  diastolic  pressure  fall,  when  it  occurs,  will  be  either  a 
slow  controlled  drop  or  of  the  rapid  fainting  type  which  is  often 
spoken  of  as  a  break  in  the  circulation. 

Candidates  are  rated  A  A  if  the  compensations  are  good  down  to 
7  per  cent  or  less  and  A  if  good  to  between  8  and  7  per  cent.  They 
are  rated  B  if  the  compensatory  mechanisms  show  decided  insuffi- 
ciency or  failure  between  10  and  8  per  cent,  and  C  if  the  failure 
occurs  above  10  per  cent  oxygen.  The  physiologist  rarely  finds 
reason  for  placing  a  candidate  in  class  D.  A  high  systolic  pressure, 
150  millimeters  and  above,  throughout  the  greater  part  of  the  test 
disqualifies  the  candidate  for  class  A  no  matter  whether  he  com- 
pensates well  or  not. 

THE   PRELIMINARY    PULSE    AND    BLOOD   PRESSURE    STUDY. 

The  candidate  reclines  for  five  minutes.  The  heart  rate  is  then 
determined  by  counting  the  pulse  rate  by  20-second  intervals. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  237 

Counting  should  continue  until  two  successive  intervals  give  the  same 
result.  The  arterial  pressures  are  then  determined.  The  candidate 
then  stands,  the  heart  rate  is  counted  as  before  until  it  reaches  a  con- 
stant rate,  when  it  is  recorded,  and  the  blood  pressures  then  taken. 

The  candidate  then  raises  himself,  by  placing  his  right  foot  on  a 
chair,  five  times  to  the  standing  position  on  the  chair.  The  pulse 
rate,  with  the  candidate  standing,  is  immediately  counted  and  as 
soon  as  possible  thereafter  the  blood  pressures  are  determined.  The 
candidate  stands  at  ease  for  two  minutes,  after  which  the  pulse  rate 
and  the  blood  pressures  are  again  determined. 

The  purpose  of  these  observations  is  to  determine  whether  the  can- 
didate shows  evidences  of  staleness.  In  the  physically  fit  the  heart 
rate  does  not  increase  much  on  standing,  but  in  the  wearied  or  phys- 
ically stale  it  increases  as  much  as  44  beats  per  minute.  The  vaso- 
motor  control  of  the  splanchnic  area  responds  to  changes  in  posture. 
In  the  fit  subject  the  splanchnic  vasotone  increases  and  the  blood 
pressure  is  raised  about  10  millimeters  when  he  moves  from  the  hori- 
zontal to  the  upright  standing  posture.  Weakness  is  shown  by  a 
decrease  in  blood  pressure  and  at  other  times  by  an  excessive  increase 
in  the  heart  rate.  A  great  acceleration  in  the  pulse  rate  following 
the  exercise  is  also  a  result  of  staleness.  The  systolic  pressure  should 
return  to  normal  within  two  minutes.  The  subnormal  pressure,  and 
the  length  of  time  it  continues  after  exercise,  has  been  attributed  to 
lack  of  condition. 

PREPARATION  OF  THE  REBREATHING  MACHINE. 

(1)  Flush  the  tank  to  remove  all  vitiated  air.    Do  this  as  follows: 
Close  the  gate  valve  under  the  CO2  absorber,  and  also  the  valve  in  the 
return  pipe.    Open  the  valve  on  the  spirometer  pipe.     Open  the 
inlet  valve  of  the  water  system  and  allow  the  tank  to  fill  slowly. 
When  the  tank  is  full,  raise  and  lower  the  spirometer  drum  several 
times  to  change  the  air  in  its  dead  space. 

(2)  Fill  the  tank  with  new  air  as  follows :  Open  the  gate  valves  in. 
the  air  pipes  and  close  the  valve  in  the  spirometer  pipe.    Let  the 
water  drain  entirely  out.     Set  the  valves  as  before  and  refill  with 
water  a  second  time.    Let  drain  as  before  to  the  desired  level. 

(3)  Set  the  machine  for  the  start  by  opening  the  valves  in  the  air 
pipes  and  closing  the  valve  in  the  spirometer  pipe. 

(4)  Sterilize  the  mouthpiece  by  bringing  it  to  the  boiling  point. 
See  that  the  corrugated  rubber  hose  is  clean  and  dry. 

PREPARATION   OF  THE   RECORDING   APPARATUS. 

The  excursions  of  the  spirometer  indicate  the  depth  and  rate  of 
breathing  of  the  subject.  A  fishline  connected  to  the  top  of  the 
spirometer  runs  over  a  pulley  and  fastens  to  a  counterbalance  for 


238  MANUAL  OP  MEDICAL  RESEARCH   LABORATORY. 

the  spirometer  can.  A  writing  point  is  attached  to  the  coun- 
terbalance and  records  the  respiration  on  the  smoked  drum  of  the 
kymograph.  The  writing  point  is  best  cut  from  celluloid  film.  The 
angle  of  the  point  should  not  be  less  than  60  degrees  because  very 
acute  points  twist  easily.  The  point  may  be  attached  to  an  aluminum 
stylus  by  means  of  beeswax. 

A  signal  magnet,  provided  with  a  writing  point  and  connected  in 
series  with  two  cells  and  a  clock  interrupter,  records  equal  intervals  on 
the  revolving  drum — usually  half  minutes. 

SMOKING  THE  DRUM. 

Lay  the  kymograph  paper  on  the  table,  glazed  side  down  and  glued 
end  away.  Hold  the  drum  with  the  top  to  the  right  and  lay  it  across 
the  middle  of  the  paper.  Bring  both  ends  of  the  paper  toward  each 
other,  letting  the  glued  end  overlap.  Glue  it  firmly  to  the  glazed  side 
of  the  unglued  end  so  that  the  paper  is  wrapped  tightly  around  the 
drum. 

Smoke  the  drum  over  a  4-inch  single-burner  oil  stove,  or  a  fish- 
tail gas  burner.  Hold  the  axis  of  the  drum  in  each  hand  and  let  the 
drum  revolve  rapidly  toward  you,  moving  the  drum  from  side  to 
side  at  the  same  time.  Smoke  it  only  until  it  is  coated  light  brown. 

Arrange  the  drum  so  that  the  writing  point  attached  to  the  spirom- 
eter and  that  of  the  signal  magnet  will  mark  evenly  on  the  drum. 
The  stylus  of  the  signal  magnet  should  be  about  1  centimeter  above 
the  lower  edge  of  the  drum  and  about  1  centimeter  in  front  of  the 
spirometer  stylus. 

OPERATION  OF  THE  MACHINE. 

Let  the  subject  sit  so  that  the  mouthpiece  can  be  held  comfortably 
in  the  mouth  without  twisting  or  pulling  in  any  direction.  Close  the 
signal  magnet  switch.  Start  the  kymograph.  See  that  the  valves  in 
the  pipes  are  open  and  that  the  gate  valve  in  the  spirometer  pipe  is 
closed.  Put  on  the  nose  clip.  The  physiologist  will  start  the  experi- 
ment by  putting  the  cork  in  the  mouthpiece  at  the  end  of  an  expira- 
tion. The  stop  watches  should  be  started  at  this  time. 

As  the  experiment  progresses  the  oxygen  from  the  tank  is  used 
up  progressively.  The  spirometer  stylus  will  write  nearer  the  top 
of  the  drum.  Open  the  inlet  valve  in  the  water  system  and  let  a 
little  water  flow  into  the  tank,  sufficient  to  bring  the  writing  point 
nearly  to  the  bottom  of  the  drum.  Repeat  this  as  often  as  necessary. 

When  the  experiment  is  ended  close  the  valves  in  the  air  pipes 
until  the  air  samples  are  taken. 

Write  the  name  of  the  subject,  date,  and  type  of  experiment  on  the 
smoked  drum.  It  is  also  convenient  to  record  the  oxygen  per  cent. 
Kemove  the  paper  by  cutting  through  the  outer  sheet  at  the  lap. 


MANUAL  OF   MEDICAL  KESEABCH   LABORATORY.  239 

Do  not  cut  through  both  sheets  and  scar  the  drum.  Hold  the  paper 
by  each  end,  smoked  side  up,  and  pass  it  once  through  a  shellac 
solution.  Hang  it  up  to  dry. 

CARE  OF  THE  APPARATUS. 

Leaks.— If  a  leak  is  suspected  from  the  character  of  the  respira- 
tion record,  first  see  that  the  valves  of  the  water  system  are  closed. 
A  leak  of  water  into  the  tank  through  the  inlet  valve  will  make  the 
lower  level  of  the  respiration  tracing  approach  the  horizontal.  A 
leak  of  water  out  of  the  tank  through  the  drain  valve  will  make  the 
record  approach  the  perpendicular. 

Leaks  of  air  out  of  the  system  most  frequently  occur  around  the 
mouthpiece.  It  may  be  necessary  to  tape  the  rubber  portion  to  the 
metal  part.  Leaks  of  air  around  plumbing  joints  may  be  stopped  by 
using  white  lead  or  heavy  paint. 

The  COZ  absorber. — This  is  a  cylindrical  pasteboard  carton  filled 
with  shell  sodium  hydroxide.  This  cartridge  is  contained  in  a  steel 
case  and  is  easily  replaced.  It  is  effective  in  removing  CO2  for  about 
200  to  240  minutes  of  rebreathing.  If  the  cartridge  becomes  very 
warm  or  the  subject  breathes  excessively  do  an  analysis  for  CO2,  and 
if  it  is  present  reject  the  cartridge.  Before  each  experiment  the 
resistance  of  the  cartridge  to  expired  air  should  be  tried  by  blowing 
through  the  cartridge  with  the  air  valve  below  it  open  and  the  other 
valves  closed.  The  spirometer  can  be  easily  raised  if  the  sodium 
hydrate  is  not  caked. 

When  a  new  cartridge  is  inserted,  punch  both  ends  full  of  holes 
with  a  pencil,  put  the  loose  brass  ring  inside  the  lower  rim  of  the 
pasteboard  cartridge,  put  the  rubber  gasket  around  the  outside  of  the 
lower  rim,  put  the  cartridge  with  the  marked  end  up  into  the  steel 
case  and  tighten  the  thumb  screws.  Do  not  use  a  cartridge  without 
a  brass  ring  and  always  remove  brass  ring  before  rejecting  a  used 
cartridge. 

Shellac. — Make  a  saturated  solution  of  powdered  shellac  and  de- 
natured alcohol  containing  about  1  teaspoonf  ul  of  castor  oil  to  each  2 
quarts  of  alcohol.  The  mixture  should  be  shaken  thoroughly  and  a 
residue  of  undissolved  shellac  should  always  remain  in  the  bottom 
of  the  bottle.  If  the  records  appear  running  after  shellacing,  the 
solution  probably  needs  more  shellac.  Do  not  allow  the  shellac  to 
stand  exposed  to  the  air  except  while  it  is  being  used.  The  castor 
oil  makes  the  dried  record  more  flexible. 

Kymograph. — The  kymograph  consists  of  an  aluminum  drum  re- 
volved by  means  of  a  clockwork  at  its  base.  The  drum  slides  on  a 
brass  sleeve  and  is  held  at  any  desired  height  by  a  spring  clip.  The 
sleeve  ends  in  a  friction  plate  which  rests  on  a  metal  disk  driven  by 
the  clockwork.  The  sleeve  and  friction  plate  revolve  about  a  steel 


240  MANUAL  OF  MEDICAL  RESEAECH  LABORATORY. 

shaft  which  passes  through  both  of  the  heavy  plates  containing  the 
clockwork  and  is  bolted  at  the  bottom  plate.  At  the  top  of  the 
sleeve  is  a  screw  by  means  of  which  the  drum  and  sleeve  may  be 
lowered  until  the  friction  plate  rests  upon  the  metal  disk.  It  is 
always  used  in  this .  position  when  driven  by  the  clockwork. 

In  the  clockwork  are  a  pendulum  and  a  ratchet  wheel  which  pro- 
vide for  a  slower  speed  than  can  be  obtained  by  any  of  the  fans. 
It  may  be  thrown  in  gear  by  raising  the  pin  in  the  gear  peg  out  of 
the  hole  in  which  it  rests.  When  the  screw  near  the  fan  pinion  is 
screwed  down  the  clockwork  operates  as  a  medium-spring  kymo- 
graph. When  this  screw  is  up  the  drum  revolves  approximately 
once  an  hour,  which  is  the  speed  used  for  rebreathing  work. 

CALIBRATION  OF  THE  SPIROMETER. 

In  order  that  the  volume  of  air  breathed  during  any  period  may 
be  determined,  the  relation  between  the  definite  volume  of  air 
breathed  and  a  certain  linear  measure  (1  centimeter,  for  example) 
on  the  kymograph  must  be  established. 

To  calibrate  the  spirometer,  remove  the  can  and  fill  it  with  water 
to  a  depth  of  25  centimeters,  measuring  with  a  graduate  the  amount 
of  water  used.  If  a  liter  or  cubic  centimeter  measure  can  not  be 
obtained,  use  a  quart  or  a  pint  measure.  (One  quart  equals  1.36  liters ; 
1  pint  equals  0.568  liter;  1  fluid  ounce  equals  28.66  cubic  centi- 
meters.) Divide  the  volume  in  cubic  centimeters  by  the  depth  of 
the  water  and  the  quotient  will  be  the  volume  contained  in  the  can 
per  centimeter  of  length.  To  make  the  relation  scale,  let  1  centi- 
meter be  equivalent  to  the  volume  determined  above.  This  may 
be  attached  to  the  spirometer  so  that  the  pointer  will  pass  over  the 
scale  on  each  respiration.  Or  it  may  be  used  for  plotting. 

THE  GAS  ANALYZER. 

DESCRIPTION   OF  APPARATUS. 

The  apparatus  consists  essentially  of  a  25  cubic  centimeter  gas  bu- 
rette with  a  bulb  containing  about  17  cubic  centimeters  and  a  tube  be- 
low graduated  from  18  to  25  cubic  centimeters  in  0.02  cubic  centi- 
meter, so  that  it  can  be  read  easily  to  0.01  cubic  centimeter.  The  lower 
end  of  the  burette  connects  with  a  temperature-control  tube  similar 
to  the  gas  burette,  but  not  graduated,  and  a  leveling  bottle  containing 
1  to  2  per  cent  sulphuric  or  other  acid  in  50  per  cent  alcohol.  The  top 
of  the  burette  communicates  (by  means  of  a  capillary  tube)  with  an 
absorber  for  carbon  dioxide  containing  10  per  cent  sodium  hydroxide, 
and  a  similar  absorber  for  oxygen,  containing  a  solution  of  pyrcgal- 
lic  acid  in  nearly  concentrated  potassium  hydroxide. 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  241 

There  are  four  glass  stopcocks  which  must  always  work  freely.  A 
two-way  stopcock  is  situated  on  a  T  just  above  the  gas  burette  by 
means  of  which  a  sample  may  be  taken  and  a  contaminated  sample 
expelled.  A  one-way  stopcock  is  situated  just  above  the  bulb  of 
the  control  tube  and  should  always  be  kept  closed  during  an  analy- 
sis. A  one-way  stopcock  is  situated  above  each  of  the  absorbers 
and  should  always  be  kept  closed  except  when  the  particular  ab- 
sorber is  in  use. 

Around  the  two  bulbs  is  a  jacket  which  is  filled  with  water  at  room 
temperature.  The  water  in  the  jacket  can  be  mixed  by  blowing  air 
through  a  glass  tube  passing  to  the  bottom.  It  is  important  to  keep 
the  water  thoroughly  mixed  in  order  to  insure  the  same  temperature 
and  water-vapor  tension  in  the  gas  burette  and  the  control  tube  at 
the  time  of  an  experiment. 

USE  OF  THE  APPARATUS. 

1.  Before  an  analysis  is  begun  it  must  be  assured  that  the  capillary 
tubes  between  the  gas  burette  and  the  absorbers  contain  nitrogen. 
This  is  the  case  after  an  analysis  for  CO2  and  O2,  and  it  may  be 
necessary  to  do  an  analysis  for  this  purpose. 

2.  At  the  beginning  of  an  analysis  the  level  of  the  sodium  hy- 
droxide and  the  alkaline  pyrogallate  in  the  absorbers  should  be  a  cer- 
tain height  marked  by  a  wire.   The  level  may  be  adjusted  with  all  the 
stopcocks  closed,  except  that  to  the  particular  observer  in  which  the 
level  is  being  adjusted.     The  leveling  bottle  is  carefully  raised  or 
lowered  and  the  stopcocks  closed  when  the  meniscus  of  the  fluid  comes 
to  the  wire,  or  the  wire  may  be  set  to  the  meniscus.     After  an 
absorption  the  level  is  again  adjusted  to  the  wire. 

3.  The  level  of  the  fluid  in  the  control  tube  is  next  adjusted.    A 
strip  of  millimeter  paper  is  pasted  on  the  leveling  bottle.    The  top 
of  the  gas  burette  and  the  control  tube  are  opened  to  the  outside  air. 
The  leveling  bottle  is  lifted  a  short  distance  so  that  the  level  of  the . 
fluid  in  the  control  tube  comes  somewhere  between  24  and  25  on  the 
scale  of  the  gas  burette.    The  level  of  the  fluid  in  the  control  tube 
and  that  in  the  leveling  bottle  should  be  the  same,  and  the  point  is 
marked  by  the  sliding  wire.     The  stopcock  on  the  control  tube  is 
then  closed  and  kept  closed  during  the  remainder  of  the.  analysis. 

4.  The  stopcock  at  the  top  of  the  gas  burette  is  open  to  the  outside 
air  and  the  leveling  bottle  is  lifted  until  the  gas  is  expelled  from  the 
burette  and  a  few  drops  of  fluid  run  out.    The  stopcock  is  then  turned 
so  as  to  communicate  with  the  source  of  gas,  and  a  sample  is  then 
taken  by  lowering  the  leveling  bottle.    The  sample  may  be  driven 
back  into  the  collector  several  time  to  insure  a  representative  por- 
tion.   The  stopcock  is  closed.    The  time  is  noted  at  which  the  column 
of  fluid  falls  in  the  gas  burette,  and  no  reading  is  taken  until  exactly 
two  minutes  have  elapsed.    This  is  to  insure  proper  drainage  of  fluid 

8911&— 18 16 


242  MANUAL  OF  MEDICAL  RESEARCH   LABORATORY. 

from  the  inside  of  the  tube.    If  large  drops  stand  on  the  inside  after 
two  minutes  the  tube  needs  cleaning. 

5.  Before  reading  the  volume  of  the  sample,  or  later,  when  reading 
the  volume  of  the  residual  gas  in  the  burette,  the  leveling  bottle  is 
moved  up  or  down  on  the  control  tube  until  the  level  of  the  liquid 
in  the  control  tube  comes  to  the  wire.    By  means  of  the  millimeter 
paper  strip  note  is  made  of  the  height  above  or  below  the  meniscus 
in  the  control  tube  at  which  the  bottle  must  be  held  to  bring  the  gas 
in  the  control  tube  to  its  original  volume  (at  the  wire) .    The  leveling 
bottle  is  then  held  at  the  same  height  above  or  below  the  meniscus  in 
the  burette  and  a  reading  taken.    In  this  way  the  gas  in  the  burette 
can  always  be  brought  to  the  correct  volume  per  molecule. 

6.  The  sample  is  now  driven  into  the  CO2  absorber.     (Samples 
from  the  rebreathing  machine  should  not  contain  CO2,  so  this  step 
may  be  omitted  and  the  O2  absorption  carried  out  directly.)     With 
the  leveling  bottle  above  the  level  of  the  fluid  in  the  burette,  the 
stopcock  above  the  CO2  absorber  is  opened  and  the  bottle  lifted  in 
order  to  drive  the  sample  into  the  absorber.    The  gas  is  driven  over 
eight  or  ten  times,  after  which  the  bottle  is  lowered  carefully  until 
the  level  of  the  sodium  hydroxide  in  the  capillary  tube  comes  up  to 
the  wire.    The  stopcock  is  closed.    A  reading  of  the  remaining  vol- 
ume is  taken  in  the  usual  manner  after  two  minutes.     The  difference 
in  volume  divided  by  the  original  volume  and  multiplied  by  100 
gives  the  per  cent  of  CO2  in  the  sample. 

7.  The  oxygen  absorption  is  now  carried  out  in  a  similar  manner, 
the  level  of  the  alkaline  pyrogallate  being  brought  back  to  the  wire 
and  the  stopcock  closed  before  a  reading  of  the  residual  volume  is 
made.    This  volume  subtracted  from  the  volume  remaining  after  the 
CO2  has  been  absorbed  (or  from  the  original  volume  if  the  sample  is 
ordinary  uncontaminated  air)  gives  the  volume  of  O2  in  the  sample, 
which,  when  divided  by  the  original  volume  times  100,  gives  the  per 
cent  of  O2  in  the  sample. 

Example:  Volume  of  sample         24.  00 
After  CO2  absorption  22.  52 

1. 48—  6.  17  per  cent  CO2 
After  O2  absorption      19. 14 

3. 38—14. 08  per  cent  O2. 

SUMMARY  OF  THE  PROCEDURE  FOR  AIR  ANALYSIS. 

1.  Be  sure  that  the  capillary  tube  contains  nitrogen. 

2.  Bring  the  level  of  the  sodium  hydroxide  and  the  alkaline  pyro- 
gallate in  the  capillary  tubes  to  their  respective  wires,  or  set  the  wires 
to  the  menisci. 


MANUAL  OF   MEDICAL  RESEARCH  LABORATORY.  248 

3.  Set  the  level  of  the  temperature-control  tube. 

4.  Take  the  sample. 

5.  After  two  minutes  read  the  volume  of  the  sample. 

6.  Absorb  the  CO2.    Bring  the  sodium  hydroxide  to  the  wire.    Head 
the  volume  after  two  minutes.     (Samples  from  the  rebreathing  ma- 
chine do  not  ordinarily  contain  CO2,  so  this  step  may  be  omitted.) 

7.  Absorb  the  O2  and  bring  the  pyrogallate  to  the  wire.    Read  the 
volume  after  two  minutes. 

CARE  OF  THE  APPARATUS. 

Cleaning. — Whenever  large  drops  stand  on  the  inside  of  the  glass 
burette  and  temperature-control  tubes  two  or  three  minutes  after 
the  fluid  has  fallen,  it  is  an  indication  that  the  tubes  need  cleaning. 
This  may  be  done  by  drawing  cleaning  fluid  into  the  tubes.  The 
tubes  must  first  be  drained  by  opening  the  stopcocks,  lowering  the 
leveling  bottle  and  disconnecting  it.  The  fasteners  at  the  top  and 
bottom  of  the  burette  should  be  removed  and  the  rubber  discon- 
nected at  the  top  of  the  burette.  This  will  allow  the  burette,  con- 
trol tubes,  and  jacket  to  be  moved  forward  in  the  slot  as  one  piece. 
The  lower  free  ends  of  the  two  tubes  may  then  be  put  in  a  beaker  of 
cleaning  fluid  and  the  solution  sucked  up  by  means  of  rubber  tubing 
attached  to  the  top  of  the  tubes.  This  solution  should  stand  in  the 
tubes  several  hours,  or  even  over  night.  All  traces  of  cleaning  fluid 
are  removed  by  repeatedly  filling  the  tubes  with  water. 

The  capillary  tubing  may  be  cleaned,  after  dismounting  it,  by 
washing  it  out  with  cleaning  fluid,  rinsing  it  with  water,  and  drying 
out  with  alcohol. 

Formula  for  cleaning  fluid. — The  cleaning  fluid  commonly  used 
consists  of  a  strong  solution  of  sulphuric  acid  in  which  potassium 
bichromate  is  dissolved.  A  layer  of  solid  bichromate  should  always  be 
kept  in  the  bottom  of  the  bottle.  This  solution  can  be  used  over  and 
over  again. 

Stopcocks. — The  stopcocks  should  always  work  freely,  but  should 
never  be  loose  enough  to  leak.  A  light  layer  of  vaseline  or  preferably 
of  a  lubrication  mixture,  should  be  rubbed  on  the  stopcocks.  Too 
much  lubricant  is  liable  to  plug  the  capillary  tubes.  A  good  grease 
is  made  by  melting  vaseline  and  beeswax  in  the  proportions  of  3  to  1. 
Another  formula  is  as  follows  (Dennis,  Gas  Analysis,  p.  115) : 

1.  Melt  together  12  parts  by  weight  of  vaseline  and  1  part  of  par- 
affin.   Do  not  heat  enough  to  give  off  fumes. 

2.  Take  parts  by  weight  of  finely  chopped  soft  black  rubber. 
Add  No.  2  to  No.  1  slowly  as  the  latter  is  dissolved,  while  heating 

over  a  low  flame.  When  most  of  the  rubber  is  added,  test  it  by  pull- 
ing it  between  the  thumb  and  forefinger.  When  it  is  of  the  right 
consistency  it  should  pull  into  cobwebby  threads. 


244  MANUAL  OF   MEDICAL  RESEARCH   LABOBATORY. 

Rubber  connections. — Rubber  connection  pieces  should  be  removed 
before  cleaning  fluid  is  used.  If  the  rubber  sticks  to  the  glass  it  may 
be  loosened  by  inserting  the  point  of  a  penknife  between  the  tube  and 
the  glass.  A  drop  of  water  put  under  the  knife  blade  sometimes 
helps.  New  rubber  connections  will  slip  on  easily  if  the  end  of  the 
glass  tubing  is  moistened  with  water. 

If  a  leak  in  the  system  is  suspected,  raise  the  leveling  bottle  until 
the  sample  tube  is  filled  with  about  18  cubic  centimeters,  close  all 
the  stopcocks  and  lower  the  leveling  bottle  as  far  as  possible.  Read- 
ings of  the  maniscus  from  time  to  time  will  be  the  same  if  no  leak  is 
present.  If  the  level  of  the  sodium  hydroxide  and  the  alkaline 
pyrogallate  in  the  capillary  tubes  will  not  stay  at  the  wire  when  the 
stopcocks  are  closed,  either  the  rubber  connections  or  the  stopcocks 
are  leaking. 

Red  rubber  should  not  be  used  on  the  connections  where  alkali 
will  touch  it,  as  it  gives  off  sulphur,  which  may  finally  appear  as 
hydrogen  sulphide  in  the  burette. 

It  may  be  necessary  to  make  the  rubber  connections  tight.  This 
may  be  done  with  a  flexible  wire,  or  more  conveniently  with  rubber 
bands.  Loop  the  band  around  the  rubber  tube,  pull  tight,  and  wrap 
the  free  end  around  the  tube  several  times,  finally  passing  it  under 
the  wrapping  with  the  aid  of  the  curved  forceps. 

A  check  on  calibration,  tightness  on  joints,  and  the  efficiency  of 
absorbents  can  be  made  by  analyzing  atmospheric  air.  If  the  appa- 
ratus is  properly  graduated  and  in  good  order,  the  sum  of  the  oxy- 
gen and  the  carbon  dioxide  in  uncontaminated  atmospheric  air  should 
be  20.96  per  cent. 

The  scale  etched  in  the  burette  tube  may  be  made  more  visible  if 
blue  crayon  is  rubbed  on  it  and  a  piece  of  white  paper  put  behind  it 
but  not  pasted  on  the  burette. 

The  analyst  must  remember  that  the  accuracy  in  the  use  of  the 
apparatus  depends  more  on  making  sure  that  absorptions  are  com- 
plete than  upon  extreme  effort  to  read  the  burette  as  finely  as  pos- 
sible. It  is  essential,  therefore,  after  an  absorption  is  supposedly 
complete,  to  pass  the  gas  over  again  into  the  absorbent  and  make 
another  reading  to  be  sure  that  no  change  occurs. 

Solutions  used  as  absorbents. — A  10  per  cent  solution  of  sodium 
hydroxide  is  used  to  absorb  CO2.  A  10  per  cent  solution  signifies 
that  in  each  100  grams  of  solution  there  are  10  grams  of  the  substance 
dissolved.  Weigh  out  about  10  grams  of  sodium  hydroxide  and  add 
water  to  make  100  cubic  centimeters. 

The  absorbent  for  oxygen  consists  of  pyrogallic  acid  in  a  nearly 
concentrated  potassium  hydroxide  solution  in  the  proportions  of  10 
grams  of  pyrogallic  acid  in  each  100  cubic  centimeters  of  KOH  of  a 
specific  gravity  of  1.55.  A  hydrometer  may  be  used  to  make  up 


MANUAL  OF   MEDICAL  RESEARCH   LABORATORY.  245 

the  KOH  solution,  or  767  grams  of  1,000  cubic  centimeters  of  water 
gives  a  specific  gravity  of  1.55. 

The  absorber  should  be  about  two-thirds  filled  with  the  absorbent, 
and  a  one-quarter  inch  layer  of  liquid  petrolatum  should  be  used  to 
protect  the  absorbent  from  the  air.  One  filling  with  alkaline  pyrogal- 
lic  will  last  for  more  than  100  analyses.  When  the  O2  absorption  be- 
comes sluggish,  .the  pyrogallate  should  be  changed,  but  mere  stand- 
ing in  the  pipette  does  not  cause  it  to  deteriorate.  The  pyrogallate 
should  be  made  more  exactly  in  the  manner  described,  for  both  weaker 
and  stronger  solutions  do  not  absorb  so  well. 

In  renewing  the  sodium  hydroxide  or  the  alkaline  pyrogallate, 
care  should  be  taken  not  to  get  the  oil  on  the  absorbing  surfaces. 
This  may  be  avoided  by  first  removing  the  oil  with  a  pipette.  Or  it 
may  be  necessary  to  siphon  off  the  greater  part  of  the  old  solution 
through  the  capillary  tube.  In  this  case  the  lower  surface  of  the 
oil  should  not  be  allowed  to  come  to  the  lower  edge  of  the  absorbing 
tube.  New  solution  may  then  be  added  through  the  capillary  tube 
and  the  oil  will  remain  on  top  and  inside  of  the  absorbing  tube  as 
before. 

It  has  been  found  convenient  to  use  in  the  leveling  bottle  a  1  per 
cent  to  2  per  cent  sulphuric-acid  solution  in  50  per  cent  ethyl  alcohol. 
The  alcohol  reduces  the  surface  tension  and  permits  more  rapid  and 
thorough  drainage.  It  also  acts  as  a  self -cleaner  for  the  burettes. 


INDEX. 


Page. 

Absorbents,  solutions  used  as 244, 245 

Accidents: 

Error  of  judgment  as  cause  of 137 

Physical  defects  cause  of  90  per  cent  of 77 

Acclimatization,  value  of  factors  of 30-32 

Adenoids 105 

After-nystagmus  times,  with  successive  rotations,  decrease  of 186 

Air  analysis,  summary  for  the  procedure  for 242, 243 

Air  Medical  Service: 

Organization  of 98 

Requirements  fixed  by  Chief  Surgeon  as  to  physical  condition  of  men  se- 
lected         98 

Requirements  of  the  individual  for  efficiency  of 163, 164, 165, 166 

Altitude: 

Changes,  adaptive 12 

Changes,  alveolar 25 

Effect  of,  on  the  eye 140 

Effect  of,  on  man  and  animals 7 

High— 

Ability  to  withstand 32 

Blood  concentration  at 15 

Circulation  at 16 

Comparisons  of  ventilation  of  lungs  at,  and  at  sea  level 24 

Comparisons  of  athletic  and  nonathletic  individuals  in  withstanding.        33 

Effect  on  man  during  residence  on  Pike's  Peak 16 

Fall  in  alveolar  dioxide  pressure 27 

Increased  ventilation  of  lungs  at 27 

Oxygen  pressure  of  arterial  blood  at 29, 30 

Physical  fitness  -to  withstand 32, 33 

Respiration  at 23 . 

Sequence  in  blood  changes  at 14 

Limits,  outline  of  conditions 166 

Physiology 7 

Relation  of,  pressure,  and  oxygen 36 

Respiratory  observations 28, 29 

Sickness,  cause  of 37 

Alveolar  air: 

Altitude  changes 25 

Analysis  of,  during  rebreathing  test 46 

Partial  pressure  of  gases  in 25 

Percentage  of  gases  in 25 

Pressures,  experiments  made  to  show  changes  in 68 

Apparatus,  rebreathing,  care  of 239 

Arterial  pressures - 16, 18 

Greater  at  high  altitudes 22 

247 


248  INDEX. 

Page. 

Arrhythmia 88 

Arteriosclerosis 87 

Asphyxiation,  psychological  effects  of 165 

Association  reaction  times -  -  - 199, 200 

"  Athletic"  hearts .'...' 96 

Auditory  tests 185, 186 

Average  wedge,  per  cent  transmission  and  density  of 232 

Aviation: 

Classification  of  personality  record 210, 211, 212 

Individual  fitness  for,  cases  cited 201, 202,  203,  204 

Problems  of,  psychological  investigations  of 186 

Special  conditions  to  which  the  flier  may  be  subjected 165 

Unfitness  for,  classification  of  personality  rating 209 

A — Safe,  nervous,  and  mentally  stable 209 

B— Safe,  with  limitations ^ 209 

C — Questionable ;  no  definite  conclusion  reached 210 

D — Needs  special  attention 210 

E— Unsafe 210 

Aviation  Service,  casualty  list,  reduction  of  methods  for 204,  205 

Aviator: 

Advice  on  keeping  nerve 205, 206 

Deterioration  of,  causes  of 166 

Physical  examinations  of  applicants  in  first  call 133-136 

Practical  requirements 168 

Psychological  qualifications  of 178, 179 

Rating  tests 1 68, 169, 170 

Routine  monthly  examination  of  the  eye  of,  suggested 231 

Supervision  of 207 

Balloon  ascention,  historic  experience  in,  by  Tissandier 10 

Barometric  pressure 21 

Blood  changes  at  high  altitude 13, 14 

Blood  circulation: 

"Athletic  "hearts 96 

Arrhythmia 88 

Anteriosclerosis 87 

Changes  of,  causes  of 21 

Circulatory  collapse 83 

Effects  of  low  atmospheric  pressure  on 75-90 

Effect  of  low  oxygen  tension  on  circulatory  physiology 78 

Effects  on  pathological  cases 87 

Heart  strain 83,  84 

Increasing  the  blood  flow 80 

Insufficient  compensation 82 

Oxygen  deficiency,  compensation  for 79 

Physiology  of 77 

Pike 's  Peak,  blood  circulation  observations  made  on 43 

Pulse  rate  as  indicator  of  oxygen  want 43 

Rate  of  flow  of  blood 20,43 

Observations  made  on  Pike's  Peak 43 

Respiration,  increase  in 79 

Sequence  in  blood  changes  at  high  altitude 14, 15, 16 

Under  a  decreasing  oxygen  supply 42-50 

Valvular  disease 96 

Vasomotor  control  of  heart 80, 81 


INDEX.  249 

Page. 

Blood,  oxygen  pressure  in ,        11 

Blood  pressure : 

After  physical  exertion 58 

Capillary 20 

Effects  of  physical  exertion  on 21, 22 

Increase  and  decrease  in,  during  rebreathing  test 47,  51 

Oxygen  pressure  of,  at  high  altitudes 29, 30 

Tests  before  and  after  a  flight 61 

Venous 16, 19 

Venous,  method  of  obtaining 50 

Breathing.    (See  Rebreathing.) 

Caloric  test 108 

Capillary  blood  pressure 16,  20 

Carbon  dioxide  capacity  of  the  blood 72 

Carbon  dioxide  in  the  blood,  effect  on  respiratory  center 23, 24 

Carbon  dioxide  pressure 25 

Chart  1 37 

Chart  2 44 

Chart  3 48 

Chart  4 51 

Chart  5 55 

Chart  6 57 

Chart  7 60 

Chart  8 62 

Chart  9 64 

Chart  9a 69 

Chart  10 65 

Chart  lOa 75 

Chart  11 89 

Chart  12 . 90 

Chart  13 91 

Chart  14 92 

Chart  15 93 

Chart  16 94 

Chart  17 95 

Chart 144 

Circulatory  changes,  causes  of 21 

Classification,  analysis  of 374 

Examinations  (table) 219 

Classification  examination 215, 216, 217,  218,  219 

Average  age  of  persons  undergoing. 219 

Directions  for 220 

Duties  of  officers 222, 223 

Routine  for  record  keeping 223, 224, 225 

Routine  for 220, 221, 222 

Code  test 181 

Comparison  of  ground  and  air  service  conditions 99 

Continuous  reaction  testa 186 

Crampton's  vasomoter  tone  index  in  rebreathing  test , 56 

Deaf-mutes,  experiments  with 113, 116 

Deep  sensibility  on  the  ground  compared  with  in  airplane 100 

Dermagraphia,  tests  for,  before  and  after  flying 208, 209 

Deterioration  of  the  individual  flier 165, 166 


250  INDEX. 

Diastolic  blood  pressure:  Pago. 

After  physical  exercise 59 

Before  and  after  a  flight 61 

Increase  and  decrease  in,  during  rebreathing  test 47, 49 

Dilution  test: 

Apparatus  used  for 39 

Comparison  of,  with  rebreathing  test 39 

Directions  for  clinician  as  to  rating 227, 228 

Distance,  judgment  of,  and  stereoscopic  vision 136, 152 

Dynamometer  test 181, 182 

Ear: 

Examination  of,  details  regarding 103 

Otologic  research  previous  to  the  war 97 

The  ear  in  "stunt"  flying 128-132 

Vertigo  effects  of  ear  stimulation 130 

Editorial  insert 193 

Equilibrium  and  orientation,  maintenance  of 164 

Equilibrium  tests 102 

Equipment,  ophthalmological ,  for  branch  laboratories 231,  232 

Eustachian  tubes,  condition  of ,  one  of  vital  importance 105 

Experiments  in  linear  upward  and  downward  directions 112-115 

Normals 112 

Deaf-mutes 113 

Tabetics 114 

Eye: 

Effect  of  altitude  on 140 

Examination ,  routine ,  during  rebreathing  test 230,  231 

Goggles,  recommendations  as  to 141 

Eye  tests: 

Accommodation  test  object 148, 159 

Apparatus  employed 161 

Binocular  field  of  vision 138 

Binocular  vision  tested  by  means  of  a  stereoscope 136 

Chart 144 

Color  vision 135,138,149,153 

Convergence  power 157 

Equilibrium,  importance  of  eye  in  maintaining 139 

External  ocular  examination 134 

Field  of  binocular  vision  and  binocular  fixation 153 

Field  of  vision 135,138,142,154 

Fundus ,  examination  of,  during  rebreathing  and  low-pressure  experiments       160 

Intraocular  tension 155 

Iris  reaction  during  rebreathing  and  low-pressure  experiments 160 

Jenning's  color  test 149 

Maddox  rod  test 146 

Muscle  balance 135,138,146 

Muscle  balance  and  muscle  strength 153 

Ocular  movements 134 

Ocular  nystagmus 134 

Ophthalmoscopic  findings 136 

Ophthalmological  examination  of  the  flier  during  low  oxygen 145 

Perception  of  motion  and  its  direction 139 

Perception  of  motion  by  the  retina 155 

Preliminary  report  of  the  research  work  of  the  ophthalmological  department      151 


INDEX.  251 

Eye  tests — Continued.  Page. 

Pupillary  reactions 134, 149 

Reaction  of  the  iris  to  light  and  accommodation 150 

Reaction  time 152 

Reeve's  wedge  test 145, 158 

Retinal  sensitivity 140, 145, 158 

Screen  and  parallax  test 147 

Stereoscopic  vision 134, 150, 152 

Tobacco,  effect  of,  upon  the  visual  acuity 152, 161 

Value  of ,  in  aviation 136-140 

Visual  acuity - 136, 138, 142, 145 

Fainting 83,84,86 

Falling  test. 108 

"Feel  of  the  airship,"  experimental  studies  on 116 

Gas  analyzer: 

Description  of  apparatus 240, 241 

Use  of  apparatus 241, 242 

Gases: 

Determination  of 26 

Intestinal 53, 54 

Goggles,  recommendations  as  to 141 

Handwriting  tests: 

Penalties  for  errors  in 182, 183 

Record  of  Pvt.  Wickman 183 

Heart: 

Arrhythmia 88 

Arteriosclerosis 87 

"Athletic"  hearts 96 

Effects  on,  at  high  altitude 76 

Effects  of  low  atmospheric  pressure  on  the  circulatory  system 75 

Efficiency  of 77 

Fainting  in  the  air 83,  84 

Output  of 20 

Increased  at  high  altitude 21 

Physiology  of  exercise  compared  with  aviation 86 

Valvular  disease •    96 

Vasomotor  control 80, 81 

Heart  beat: 

Augmentation  of,  at  high  altitudes 17 

Effect  of  physical  training  on 34, 35 

Frequency  of 45 

Rate  of,  at  14,000  feet 17 

Heart  disease,  valvular,  notes  on  the  diagnosis  of 228, 229 

Hemoglobin  in  the  blood,  occurrence  of,  during  short  exposures  to  low  oxygen.         63 

Immelmann  turn 132 

Inefficiency,  causes  leading  to 206 

Intestinal  gases 54 

Kymograph,  description  of 239, 240 

Laboratories,  branch,  ophthalmological  equipment  for 231, 232 

Lombard's  observation  on  low  and  high  altitudes 20 

Loop 131 

Low-pressure  chamber,  Mineola  laboratory 213, 214, 215 

Mathematical  tests . .  185 


252 

Medical  Research  Board: 

Members  of 6 

Organization  of 6 

Powers  of 6 

Medical  Research  Laboratory: 

Research  work  of,  in  Mineola 75 

Memory  testa 184 

Mental  hygiene,  as  related  to  aviator 207 

Motion-sensing: 

Experience  and  education  in 123 

Importance  of 100 

Observations  on,  during  airplane  flights 117-123 

Explanation  of  charts 118-123 

Motor  coordinations 99 

Motor  tendencies 173, 174 

Mountain  sickness 8, 9, 10, 11, 12 

Cause  of  symptoms 10 

Nervous  type 9 

Nervous  system,  irritability  of 35, 36 

Neurology  a^id  Psychiatry,  Department  of 200 

Nervous  and  mental  diseases 200 

Temperament 200, 201 

Neuro-psychiatric  examination 207,  208 

Nose,  examination  of,  details  regarding 104 

Nystagmus: 

Analyzed  report  on 193, 194, 195, 196, 197, 198 

Experiments 190, 191, 192 

Observation  tests 184, 185 

Ocular  movements,  effect  of  repetition  upon 186-189 

Optimum  type  of  subject 78, 83 

Orientation,  methods 198, 199 

Orientator,  otologic  apparatus  known  as,  used  in  laboratory  work 132 

Otologic  problems  under  consideration  at  the  Medical  Research  Laboratory. . .       110 

Otologic  research  previous  to  the  war 97 

Otologist,  special  care  in  selecting 98 

Oxygen: 

Blood  circulation  under  a  decreasing  supply  of 42-50 

Breathing  under  decreasing  supply  of 40-42 

Deficiency 166 

Psychological  effects  of 167 

Demands  of  body  for,  during  rapid  ascents 38 

Pressure  in  blood 11, 16,  25,  29, 30 

Pulse  rate  as  indicator  of  want  of 43 

Secretion 34 

Tension,  low,  psychological  investigations  with 180 

Physical  condition: 

Aviator 85 

Blank  for  examination 98 

Defects  cause  of  90  per  cent  of  accidents 77 

Falling  test 108 

Requirements  fixed  by  Chief  Surgeon,  Air  Medical  Service 98 

Temporary  indispositions 85 


nroux.  258 

Physical  examination:  Page. 

Adenoids 105 

Applicants  in  first  call 133-136 

Caloric  test 108 

Ear 103 

Euetachian  tubes ." 105 

Nose 104 

Nystagmus 106 

Pointing  test 106 

Results  of,  satisfactory  to  Chief  Surgeon 103 

Throat 104 

Teeth 105 

Tonsils,  condition  of 104 

Vestibular  tests 105 

Physical  examining  units,  establishment  of 98 

Physical  exercise  compared  with  aviation 86 

Physiological  data,  physiologist  to  obtain  and  interpret 234 

Physiological  responses,  rating  of 236 

Pike's  Peak: 

Blood  circulation  observations  on 43 

Effect  of  altitude  on  man 16 

Pointing  tests 106 

Pressures: 

Arterial 16, 18 

Capillary 16 

Psychologist,  instructions  to 233, 234 

Psychology  Department 163 

Psychology,  relation  of,  to  the  aviator 163 

Pulse  and  blood  pressure  study,  preliminary 236, 237 

Pulse  rate 17, 18 

After  physical  exertion 58 

As  indicator  of  oxygen  want 43 

Changes  in,  during  exposure  to  low  oxygen  pressure 73 

Effects  of  physical  exertion  on 21, 22 

Ideal  for  flying  officer,  as  stated  by  Maj .  Flack  and  Capt.  Bowdler 59 

Influence  of  posture  upon 18 

Test  for  obtaining 58 

Tests  before  and  after  a  flight 61 

Rating  scheme 175, 176, 177 

Reactor,  apparatus  for,  instructions  for 172, 173, 174 

Rebreathing  machine 212 

Adjustment  of 171 

Conditions  established  by 166 

Operation  of,  special  test 238, 239 

Preparation  of 237 

Simple  form  of 212, 213 

Rebreathing  tests: 

Alveolar  air,  analysis  of,  during  test 46 

Alveolar  air  pressures,  experiments  made  to  show  changes  in , 68 

Apparatus  for  testing  of 39 

Blood  pressure  after  physical  exertion • 58 

Carbon  dioxide  capacity  of  the  blood 72 

Comparison  of  the  rebreathing  test  and  the  dilution  test 39 


254 

Rebreathing  tests — Continued.  ge. 

Conditions  corresponding  to  altitudes  of  15,000  to  20,000  feet 66, 77 

Control  tests  to  determine  reliability  of  rebreathing  tests 67 

Crampton's  vasomotor  tone  index  used  in 56 

Deep  breathing,  advantage  of,  over  shallow  breathing 40 

Demands  of  body  for  oxygen  during  rapid  ascents 38 

Diastolic  blood  pressure — 

After  physical  exercise 59 

Increase  and  decrease  in 47, 49 

Diastolic  murmurs 228 

Directions  to  clinician  as  to  conduct  of 225, 226, 227 

Duration  of 46 

Hemoglobin  changes 72 

Incidental  results  of  work  on 177, 178 

Instructions  to  the  physiologist  as  to 234 

Intestinal  gases 54 

Length  of  time  taken  to  reach  a  low  oxygen  test 46 

Observations  made  on  Pike's  Peak  in  regard  to 26, 27 

Physiology  of  rebreathing  and  aviation 38-74 

Power  to  hold  the  breath 52 

Pulse  rate — 

After  physical  exertion 58 

Test  for  obtaining 58 

Rates  of,  under  test 40,  41 

Relative  value  of  the  compensatory  factors -. . . .  66-68, 77 

Routine  eye  examination  during 230,  231 

Skin-color  changes  during 46 

Systolic  blood  pressure — 

After  physical  exercise 59 

Increase  and  decrease  in 47, 49 

Systolic  murmurs 228 

Turning-chair  tests 102 

Vasomotor  tone  and  endurance  of  low  oxygen 56 

Venous  blood  pressure,  increase  and  decrease  in 50-52 

Method  of  obtaining 50 

Vital  capacity  of  the  lungs 52-56 

Volume  of  air  breathed  per  minute 72 

When  under  the  action  of  progressive  decrease  in  the  oxygen  supply 40-42 

Recording  apparatus,  preparation  of 237, 238 

Respiration  at  high  altitude 23 

Rubber  connections 244 

Schneider  and  Cisco's  observations  on  the  lack  of  supply  of  oxygen 20, 21 

Skin-color  changes  during  rebreathing  test 46 

Smoking  the  drum 238 

Solutions  used  as  absorbents 244, 245 

Spinning  nose  dive 131 

Spiral  maneuver 131 

Spirometer: 

Calibration  of 240 

Respiration  data  obtained  from  kymograph  record  of 234, 235 

"Stale  athlete,"  remarks  on.* 35 

"Stale  pilot,"  remarks  on 35 

Standard  test: 

Apparatus  for 170, 171 

Method  of  conducting 171, 172 


INDEX.  255 

Page. 

Stopcocks 243 

StrohPs  comparison  of  hearts  of  Alpine  and  Moor  snowbirds 23 

"Stunt"  flying 128-132 

Immelmann  turn 132 

Loop 131 

Spinning  nose  dive 131 

Tight  spiral 131 

Symbols  and  their  significance 174, 175 

Systolic  blood  pressure: 

After  physical  exercise 59 

Before  and  after  a  flight 61 

Increase  and  decrease  in,  during  rebreathing  test 47, 49 

Tactical  discrimination 181 

Throat,  examination  of,  details  regarding 104 

Teeth,  examination  of 105 

Tight  spiral  maneuver 131 

Tissandier,  description  by,  of  high  altitude  ascent 10 

Tobacco: 

Effects  of,  on  aviators 163 

Effect  of,  upon  the  eye 152, 161 

Tonsils,  examination  of 104 

Valvular  disease  of  the  heart 96 

Venous  blood  pressure 19,  20 

Increase  and  decrease  in,  during  rebreathing  test 50-52 

Method  of  obtaining 50 

Vertigo 105, 106 

Vestibular  sense,  its  motion-sensing  utility  as  great  in  the  air  as  on  the  ground. .       101 

Vision  on  the  ground  compared  with  in  the  air 100 

Whirling  artists,  dancers,  and  equilibrists,  tests  of 124, 126 


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